Clonidine has a half life of 12-16 hours ( up to 41 hours if a person has severe kidney impairment)

So its possible that the medication is dropping your blood pressure to low and your body/mind it keeping you awake so that your safe. The lingering dizzy and sleepy symptoms are probably due to the long half life.

I was given Minipress (also a blood pressure med )while IP. It has shown promise in reducing PTSD nightmares. I wasn't able to tolerate it due to my blood pressure dropping too low and I always feel nausea if that drops to low.

Just something to consider. Hope your feeling better really soon