[altruios]

Yep. During the first parts of sleep your body locks to prevent you from acting out your dreams. Here are a few:

When your body locks up, test it. try to use as much force as you can without 'breaking' that lock... it keeps you in the present moment and 'close to being able to move'...

The standard: focus on your breathing is also applicable.

What has helped the most is imagining a dot, and moving that dot around, changing its color, moving it along the z-direction (closer). Focusing your mind on that keeps it active.