Main causes of nausea at night?

What are the main causes of nausea at night?  I've been waking up between 2-4am with bad nausea, usually feeling very hot. I am not menopausal or pregnant.

While it is difficult for me to say what your exact problem is, the period of time you are getting your symptoms correlates to an increase in pitta, or excess bile.  Thus one measure would be discharge the liver of excess bile by going on a liver cleanse for a few weeks, avoiding heavy and greasy foods, and emphasizing lots of leafy green veggies.  Pay attention too to issues like food-combining, or eating foods that are hard to digest such as flour products.  You might have a food sensitivity as well, and so think about going on an elimination-challenge diet.  You can find details on all this information in my new book Food As Medicine.