[Mynder]

I suggest two possibilities that appear "plausible":

1. There really is at least one entity external to OP, and at least one of them is either truly malignant or simply wants to scare OP and have a good laugh

2. There is no evil entity external to OP. This could mean either a guide who is trying to help OP astral project or no entity at all. The sensory conviction of somebody being there could be simply OP's fear of leaving the body (there is a reason why we, for the most part, don't do that on a whim). Fears and other emotions can become tangible construcs in dreams and the astral, and it may look as if they "drain" their "creator" when in fact it's the creator actively sustaining the construct. Own your fears. Acknowledge them. Take heart, find courage, embrace and overcome them.

As I see it, OP has a choice to make, to either shut these happenings out (by using appropriate means and mantras of protection), or facing the inner fear, mentally preparing for either case, again with appropriate protection (Erin wrote what works for her, and there are many other ways to do this).

If you are utterly convinced that nothing can harm you, then you will be at the most stable and resistant to any kind of attack or energy "drain".