How to breathe into your stomach and not get light headed during meditation? During conventional Buddhist sitting meditation I have a problem whereby because I am thinking about my breathing my breath is quite short (I can't seem to change that) and just a few minutes in, just as I am starting to get into a deeper state and see something, I find that I start feeling quite light headed and almost hyperventilating because I am thinking about the breath and thus not breathing as I usually (which may still not be the perfect way for meditation, but at least normally when I'm not thinking about my breath I don't hyperventilate).

I have been told by teachers that I should try to breathe into my stomach as this is good energetically and will make the breath to the degree and the length it needs to be.

However, no matter what I try, I don't seem to be managing to achieve this stomach breathing.

So I was wondering if there is a particular knack to it or any advice? Am I actually trying to breathe into my stomach or just to expand my lungs down there (different teachers have said contradictory things on this matter)?
How to breath into your stomach and not get light headed during meditation?

When you breathe with your diaphragm (instead of just with your rib cage) you breathe more deeply.
To avoid hyperventilating then, you presumably need to breathe more slowly:


Longer pause between breaths
Longer duration during breaths (during each inhale or exhale)


Try both:


Breathe slowly (because deeply; the only time I deliberately breathe deeply and rapidly would be during vigorous exercise)
Don't be in a hurry to deliberately take/start the next breath after exhaling (instead, taking a next breath is a reaction to needing more air)


I have a problem whereby because I am thinking about my breathing my breath is quite short

"Where" are you think about your breathing: is your focus somewhere around your nose?

An alternative might be to focus somewhere lower: e.g. on your diaphragm; or lower (e.g., according to the Chinese, "The Lower Dantian (Jing), located two inches below the navel, is the source of energy which builds the physical body").

Or even lower: my Tai Chi teacher once said to imagine breathing through your heels!

In Anapanasati -- Unveiling the Secrets of Life by Bikkhu Buddhadasa, it recommends you shift your point of awareness (in Appendix D in the section titled "Getting Started: Establishing Sati"):


  Note the three primary segments of each breath: beginning, middle, and end. For the inhalation these
  correspond to the nose, the middle of the chest, and the abdomen. For the exhalation the reverse is true, beginning at the
  belly and ending at the nose. Watch and wait at the nose until the incoming breath is felt there. Then skip to the middle
  of the chest and watch there until the breath is felt. Then skip to the abdomen and watch there until the breath is felt.
  Continue watching as the inhalation ends and wait for the exhalation to begin.


That's just a preliminary practice though:


  This hopping from point to
  point is a relatively easy way to establish sati on the breath. It is a good way to get started. It becomes, however,
  somewhat crude and agitating after a while. Once we are skilled at it, we will want a more refined and peaceful way to
  be mindful of the breath


After that, it says,


  Next, we connect the three points into a continuous sweep or flow. This more closely approximates the breath
  itself. We call this "following, chasing, hunting, stalking." While breathing naturally, without any forcing or
  manipulating of the breath, sati follows the breath in and out, between the tip of the nose and the navel.


And finally:


  Once "following" becomes easy and constant, it will begin to feel unnecessarily busy and disruptive. Now we
  are ready for "guarding," a more peaceful way to practice sati with the breathing. By this time, a certain point in the
  nose will stand out.


In summary:


  If at first our breaths are short and shallow, with movement in the chest only and not in the abdomen, then simply
  follow the breath down however far it goes. After sati is established we will relax and the breathing will become deeper.
  Before long we will feel movement in the abdomen. If we see that the breath is passing by many places at the same
  time, do not use this fact as an opportunity to complicate things. Keep it simple. A simple flow from the tip of the nose
  to the navel and from the navel to the tip of the nose is sufficient for our purpose. 


These quotes are extracts; I'd recommend you read the book for a further or more complete description.

Am I actually trying to breath into my stomach

Air should go into the lungs as usual, not literally into your stomach!

I think it means to drop your diaphragm (so that the lungs expand downwards). 

When you do that there's less room (less volume remaining) for your stomach, intestines, etc.: so you need to relax your abdominal muscles (which might normally keep the belly from protruding) and let your belly appear to push forward when you breathe in.

Imagine you had a metal band, tied around your ribs, so that you couldn't inhale by expanding your rib-cage: you'd still be able to breathe by using your "stomach" (i.e. diaphragm and belly) ... that's what "breathing into the stomach" means.

To be honest what I just described seems to be contradicted by something in the Anapanasati book I referenced above (in Lecture Two, in the section titled "Step One: The Long Breath"):


  When there is a deepest
  possible long breath, does the chest expand or contract? Does the abdomen expand or contract? These are things to
  examine. In doing so, you may learn that it works differently than you thought. Most people have the overly simple idea
  that when we breathe in the chest expands and when we breathe old: the chest contracts. In studying the breath
  carefully, however, we find that in taking the longest inhalation, the abdomen will contract and the chest will expand.
  With the very long exhalation, then, the abdomen will expand and the chest will contract or deflate. We find the reverse
  of what common sense teaches. You ought to investigate this business of the very long breath, the longest possible
  breath, to see what changes happen. Do not take anything for granted. You ought to understand even these most basic
  natural facts.


This is explained later (in Appendix D, in the section titled "Long &amp; Short Breaths),


  After sati is established (techniques two or three) we begin to notice the long and short breathing. The mind still may
  wander some but stays with the breath enough to learn what it is like. The first and easiest quality to note is length, in
  terms of both time and extent of physical movement. For our purposes, an exact dividing line between short and long is
  not important. Become familiar with your own breathing and learn what your longest breaths and shortest breaths are
  like relative to each other. There is no need to compare your breaths with someone else's. (D. 29)
  
  Generally, you will find that abdominal breathing is longer than chest breathing, that is, if abdominal breathing comes
  naturally. This is something we observe, however, it is not something we desire or seek. We are not "supposed" to
  breath in a certain way and we do not use Anapanasati to develop this or that way of breathing. So do not try to force
  abdominal breathing, the results would not be very relaxing. But should it occur naturally, you will see that it is longer,
  more relaxed, and healthier. (D. 30)
  
  Should your breaths become very long, you will discover an interesting point. You may have thought it strange when
  Ajahn Buddhadasa said that the chest expands and the abdomen contracts with the long in-breath (Marker 58). Common
  sense says that the abdomen expands on the in-breath and contracts on the out-breath. The two seem to contradict each
  other. Which is right? First, we observe the normal breathing. As we inhale, the diaphragm drops and pushes the tummy
  outward. When we exhale the tummy falls in again. This is the ordinary abdominal breathing before it becomes very
  long. It is a simple movement of the abdomen expanding (or rising) with the in-breath and contracting (or falling) with
  the out-breath. Some people will consider this short and others will feel it is relatively long. (D. 31)
  
  Now, there is a limit to how far the abdomen can expand. As we relax and breathe more deeply this limit will be
  reached. At that point there is, however, room left in the chest (lungs) for more air. If we continue to breathe in, the
  chest will then expand. This in turn pulls up and flattens the tummy. This is what Ajahn Buddhadasa meant. A very
  long inhalation begins just like a normal breath. The abdomen expands but the chest barely moves at all. After the
  abdomen's limit is reached the chest expands and the abdomen contracts. When the breath is really long you will
  discover this for yourself. The opposite movements (roughly) occur with the very long exhalations. So the very long
  breath is an ordinary breath plus more. Many of us will seldom experience this very long breathing until the body 
  becomes very relaxed through Anapanasati. Eventually, it will happen more and more regularly - even outside the
  formal sittings. (D. 32)


In other words, a very long breath starts by depressing the diaphragm (abdominal breathing), and when that's full then the in-breath continues by expanding the rib-cage.