Same here... only I would describe my experience as a "panic attack in slow motion".
I'll wake up in the middle of the night... usually around 2:00 or 3:00 AM and will just lay there, unable to sleep, with incredible fear for several hours.
Elsewhere, that is what I experience too. I keep a bottle of sleeping pills and a glass of water by my bed because of this. When I wake up in the middle of the night terrified and drenched in 'cold sweat', I change my t-shirt, move to a dry part of the bed, take another pill, and go back to sleep.
Even during the day, I carry a sense of 'impending doom' and terror with me always. Work distracts from it. At night, though, is when it really all comes out. I know it sounds stupid, but, sometimes I have friends or even my dad sleep over because I'm 'scared'. I'm sort of in a constant state of panic. I think, for me, it's because I'm not sure about whether or not I'm making a mistake regarding the Witnesses.