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narcolepsy in it's classic form is when people randomly fall asleep throughout the day. One minute you are talking to them, the next their head falls and they are asleep for a minute or two, and then they wake up and are fine. In my case, if I have it, I am just excessively tired throughout the day, and I can take 2 hour naps, and still be tired the entire day. They think narcoleptics get too much REM sleep, which causes issues in wakefulness.
Sleep Apnea is when a person stops breathing throughout the night, and has to wake up (usually unbeknownst to the person, they don't fully wake up) to get them to start breathing again. So people with sleep apnea use machines that force oxygen into the airways to keep them open so they stay asleep.