dmetras: My sleep pattern is thus: 5 hrs. Wake up. When tired, fall back asleep. Wake up from vivid dream (not necessarily a nightmare) later, fall back asleep, wake up from another vivid dream.
Last time that happened (yesterday), I awoke from a nightmare that rattled me quite a bit. It left me exhausted the rest of the day, and I went to bed at 8:30. I woke up at 1 in the morning, still feeling shaken.
Now, it's slightly after 2:30 am. I'm hungry, waiting to become tired again, focused on that nightmare that has its foul grip on me. Eating now probably isn't a good idea. I'm working toward resolving the nightmare's hold on me, but the friend I need to talk to for reassurance lives in AZ (west of me) and isn't logged into Facebook, so I left a message.
If that happens that may qualify as a sleep disorder, these are worth getting tested and treated by a sleep specialist. Some are so severe they can literally cause heart failures, others will just turn you into a person you'd probably not otherwise be and certainly wouldn't want to be. If you ihave insurance it will almost certainly cover a trip to a sleep specialist.
EDIT: poor grammar, I'm drunk, sorry.