Why do I have trouble breathing & anxiety when falling asleep?

Sometimes I have trouble breathing & desperation anxiety when falling asleep. They happen at the same time when I start dozing to la-la land. It happens in perfect synchronization. Some nights I fall asleep totally normally. I don't think it's stress, although it can be. I'm chubby, but I don't think it's that. I don't think it's low glucose. I do feel brain-power drained each night, which kicks in my OCD every night, then I can't think straight. And I'm the only one I've ever encountered with this exact type of problem. I believe my breathing and desperation anxiety while dozing off is related to that evening mental drain I get almost every night. Any thoughts, people?