[Stetbrate]

i experience this myself, minus the face being seen. i usually combat this by choosing to just meditate for a while, which to me is similar in nature to napping, just awake.

i would assume that when we learn about these topics of spiritual nature, we are at a point where we are assimilating the information so well that we almost inadvertently put ourselves into a pre-meditation state.
also, if you are reading at night you already have falling asleep knocking at your door due to the chemicals your body produces when the sun is not out.

so, when you combine the 2, in my opinion, you are setting yourself up for that "sleep" state because thats where our body wants to put us when we experience slightly higher vibration for any period of time. you will feel like you want to keep learning and really try hard to stay awake, but your brain has already released the chemicals to send you off into "dream land."

my solution, as i stated, would be to simply meditate for about 30 minutes. there are benefits to it obviously, and it will help train your body to use that meditation time for relaxation, just as you would in sleep. it will also help you further your studies instead of catching z's all the time