You might have the impression you dream all night long — but that isn't necessarily the case. Find out when you're most likely to dream, based on your sleep cycle.

How the menstrual cycle affects sleep and dreams . Sleep is broken down into stages, broadly known as non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.

During "active sleep," when an octopus's skin ripples with dazzling colors, the cephalopod may experience something similar to our rapid-eye movement (REM) sleep, the authors wrote in the study ...