Your Sleep Cycle

There are 4 stages of the sleeping cycle. There is a fifth stage but that fifth stage does not repeat itself throughout the night like the others so it's not part of the "Sleep cycle". 

The sleep cycle repeats itself about 4-5 times per night but can go up to 7.

You can dream in any of the 4 stages of sleep but the most vivid and memorable dreams occur in the last stage of sleep (REM). 

This is why you can have several different dreams with a variety of different themes of each. 

But you usually dream near the morning when you are soon going to wake up. 

You may wake up and think back and not remember having any dreams but you did, you just don't remember them. 

You have several dreams a night, and you dream anywhere from 1-2 hours. 

http://www.dreammoods.com/dreaminformation/dreamresearch.htm