It sounds like you are describing the Hypnogogic State, or Hypnogogia (also spelled hypnagogia) in which people often report very vivid experiences of bizarre sensations, sounds, or sights that are similar to hallucinations and are often accompanied by the inability to move (a stage during REM when we are paralyzed. This actually protects us from leaping out of bed when we dream). But, don't concerned, they are not hallucinations as described by psychotic patients. Hypnogogic states are a normal period of sleep and usually occur during the sleep-wakefulness transitions, although we may feel that they are reality. 

These Hypnogogia are often experienced by narcoleptics but can happen to all of us. They are most noticeable, however when we are overly tired, stressed, and some medications can cause an increase in them (including muscle relaxers and antibiotics). There are also certain foods, in particular, some cheeses, that can trigger an increase in weird dreams and hypnogogia. So, be careful about eating pizza before bedtime!

One last piece; the term Hypnogogic refers to experiences while falling asleep, and Hypnopompic are the same experiences when awakening.

Hope this helps!