If you are sick before the gorilla trekking trip; you will not be allowed to trek. Sick people especially those with communicable diseases are not allowed to trek because they can easily pass on the illness to the gorillas. In Uganda and D.R.Congo you will just lose your trekking permit money but in Rwanda, if you are sick before the trekking and cannot trek, you will be refunded half your gorilla trekking permit fees.
Other non-communicable health issues if not serious cannot stop you from trekking but you should know that trekking is a tedious activity and it can cause some strain especially if you are not fit.
