Here is a dream experience submitted via my website:

“Well sometimes I would take a nap during the day or go to bed. The past two night and earlier I would take a short nap because I’m busy doing something. And I start to sleep and have a piece of a dream and I jump when I wake up. The first time in the dream I was in school and I was going to a classroom and the door slammed in my face and I woke up. The second time I don’t remember what happen. It just started happening and I’m trying to figure out why I started doing that.”

Dear Dreamer,
You could be experiencing something called a ‘hypnic jerk’ or ‘myclonic twitch’.  It’s called a hypnic jerk, or hypnogigic jerk, because it happens in the hypnogogic state – that tranistionary state between being awake and asleep.  So the dream you are having is not an R.E.M. dream, but something more similar to daydreaming (only a little deeper). In the process of falling asleep, we are entering into lower brainwave states. For some reason, that translates physiologically into the sense of ‘falling’ for a lot of us, which is why they call it ‘falling asleep’.  You didn’t mention the falling sensation, but when the body experiences this transition it is common for the muscles to contract and that can come out as legs kicking, or a feeling of jumping like when someone startles you (for example).  I don’t know if the slamming door sound really happened and you incorporated it into the dream, or if your dreaming mind created something to explain the sensation of feeling startled (this may sound weird but that dream state can be a few seconds -or more- ahead of waking time).  What is causing this? Could be irregular sleep schedules, sleep deprivation, anxiety, even drugs and medication can trigger this sensation. But the truth is nobody really knows for sure what causes this. You mentioned you are napping, so I wonder if you are on an irregular sleep schedule, and that could be the trigger.  It is likely just a temporary thing that you don’t need to worry about long term, especially if you can figure out the trigger and adjust accordingly.

I hope this helps,

Mimi