When you sleep, you do it in cycles that are about 90 minutes long. They are REM (rapid eye movement) cycles and is the brain's way of processing what has happened during the day. If you don't get enough sleep and enough REM cycles, you end up like me
When you are in a REM cycle, your body becomes paralyzed so you don't injure yourself. You might twitch occasionally but as a general rule you can't move until you get through that part of the REM cycle.
People with dogs often see this when the dog is asleep and dreaming. The dog's paws might be moving back and forth and they might be moving their lips and sometimes making funny noises, but the rest of their body remains still. This is where the animal is in REM paralysis sleep and are dreaming.
Certain foods can irritate the stomach and intestine and cause weird dreams. Cheese used to do my head in if I ate it after lunch time, but others foods can also do it. The combination of certain foods and watching certain movies can also trigger bad or unusual dreams. Stress can do it too.
You can control dreams and I used to dream of rescuing people in hostage situations and killing people. My friends used to joke about me being a sleeper agent. I put it down to being intolerant of dairy food. Who knows, maybe I am Secret Fishy, trained by the same department that made Secret Squirrel.