Morning Nightmare (4)

A couple of nights ago, I woke up at about 6:00 am after having an odd nightmare.  Once I woke up and realized what time it was, I sort of "assessed" myself because I remembered our circadian rhythm is at a high point at that time in the morning. 
When I initially woke up, naturally my heart was pounding because I had suddenly woken up from a nightmare.  Once I got myself calmed down and started thinking about circadian rhythms, I began attempting to decide if I felt energized at all.  The answer was a definite no.  After learning that teenagers' circadian rhythms are off by about two hours, I assumed that that's why I still felt exhausted.  Another factor could include that I woke suddenly in the middle of REM sleep due to my nightmare, which results in the emotions to be effected negatively (hence the racing heart and fear/anxiety once I woke).  Still another factor to my drowsiness is simply because I was still sleep deprived at that point in the morning.  Needless to say, I eventually went back to sleep that morning.
Another interesting aspect to this particular night of sleep is the context of my nightmare.  In essence, I was trying to get away from a man who was chasing me and threatening to hurt me.  Now that I know our brains allow nightmares to try and prepare us for something in the real world, I'm curious as to why my brain processed that particular nightmare.  I have not felt threatened in any way, and I don't think that a random man is going to start chasing me around (at least I hope not).  Overall, I had a pretty evenful night in terms of dreams, and knew enough about the sleep cycle to process why I felt the way I did at 6:00 am.  Yay!