I get dizzy when I dismount. Causes? Saturday I went on a ride with the local cycling club. At a certain point in the ride (after about 20 miles/32 km), I was extremely tired to the point that I decided to get off of the bike and walk for a space.

After dismounting I became so dizzy that I fell over (and don't remember falling over).

Oddly enough, I rode the same route the week before without any problems.

I am curious to know if anyone else has had this problem and what steps they took to effectively deal with it.

The two possible causes that I am already aware of are:


I am taking blood pressure medications (amlodipine and lisinopril)
I am not entirely sure my bike is a good fit; after about twenty miles I find it very difficult to find a comfortable position while riding.


I was dead-dog tired at this point in the ride (I had just gone up a fairly steep hill in a stiff headwind), and that probably exacerbated whatever is going on here.

Clarification:


I have spoken to my physician about this, about nine months ago when this first happened to me. His advice was that this was probably due to the readjustment of blood pressure after changing positions. This makes sense, as it only happens once I dismount.
My meds are for high blood pressure, so they could be doing the job too well.
I actually drank more on the ride where I was dizzy than on the ride where I was not, but the doctor has advised that I drink more, so I need to scrape together some funds for portably fluids.


Update

Went out riding with the local cycling club. I had a bit more to eat before leaving the house, and I brought along a whole lot more water, and a banana which I ate when the group stopped. I was fine until the 26-mile point, when I got a flat tire. None of the problems of the prior week appeared.

Final Update

I did the Houston MS 150 in April. I downed a banana or and equivalent amount of food at each stop, and drank my fill of water as well, and drank every time my mouth felt dry on the road. No dizziness at all.
It sounds like you over-exerted yourself and "bonked"&nbsp;&ndash; your body ran out of sugar so you fainted. In that case, you reduce the risk by eating more while you ride* and by listening to your body more and backing off when it's getting too much.

It may also be blood-pressure related: people with low blood pressure are (as I understand it) more susceptible to fainting. Since you're on blood pressure medication, you should talk to your doctor.

I don't think bike fit is really a contributor but, of course, improving that would make you a happier, more comfortable cyclist so you should do something about it even if it doesn't help the problem you most want to fix.



* In this context, snacks are not evil and you should eat them. Or, if your username indicates that you are the snack, consider eating yourself. However, this probably isn't a long-term strategy.