How to not slip into Nihilism from Vipassana? I am sensing this disenchantment from letting go. Meditating on impermanence feels like nihilism to me. There is a fleeting moment of joy from the liberation and just watching emotions go by. And I also notice the joy of it but I let it be and not cling. Then suddenly comes this pointlessness feeling. Something like nihilism. I also don't cling to that but it worries me I may lose control and just do things carelessly. 

Any guidance on this?
There are the five hindrances (also here) to meditation and practice.

Your question can be part of restlessness-worry and also doubt. But it sounds to me more like doubt.

You can read more from the essay of Ajahn Brahmavamso:


  Doubt refers to the disturbing inner questions at a time when one should be silently moving deeper. Doubt can question one's own
  ability "Can I do This?", or question the method "Is this the right
  way?", or even question the meaning "What is this?". It should be
  remembered that such questions are obstacles to meditation because
  they are asked at the wrong time and thus become an intrusion,
  obscuring one's clarity.
  
  The Lord Buddha likened doubt to being lost in a desert, not
  recognising any landmarks.
  
  Such doubt is overcome by gathering clear instruction, having a
  good map, so that one can recognise the subtle landmarks in the
  unfamiliar territory of deep meditation and so know which way to go.
  Doubt in one's ability is overcome by nurturing self confidence with a good teacher. A meditation teacher is like a coach who convinces
  the sports team that they can succeed. The Lord Buddha stated that one
  can, one will, reach Jhana and Enlightenment if one carefully and
  patiently follows the instructions. The only uncertainty is 'when'!
  Experience also overcomes doubt about one's ability and also doubt
  whether this is the right path. As one realised for oneself the
  beautiful stages of the path, one discovers that one is indeed capable
  of the very highest, and that this is the path that leads one there.
  
  The doubt that takes the form of constant assessing "Is this Jhana?"
  "How am I going?", is overcome by realising that such questions are
  best left to the end, to the final couple of minutes of the
  meditation. A jury only makes its judgement at the end of the trial,
  when all the evidence has been presented. Similarly, a skilful
  meditator pursues a silent gathering of evidence, reviewing it only at
  the end to uncover its meaning.
  
  The end of doubt, in meditation, is described by a mind which has full trust in the silence, and so doesn't interfere with any inner
  speech. Like having a good chauffeur, one sits silently on the journey
  out of trust in the driver.