Hallucinations of drowning causing lack of breathing?

I suddenly can't sleep because I'm imagining drowning(while awake) in such great detail I can neither sleep nor breathe. I had a near drowning experience around a year ago which is what making this "image" so detailed. I'm so tired and sleepy but every time I close my eyes my mind wanders back to drowning and I start choking on air. And the problem is that I'm imagining far too many scenarios at once and its gotten scary. I've never experienced this before and I don't know how to sleep.