Explanation

If you have OSA, the muscles in your throat relax and block your airways while you are asleep. This stops you from breathing for a short time. 'Obstructive' means something is blocking your airways, and 'apnoea' means 'not enough oxygen'. So OSA means there is something blocking your breathing while you are asleep. This only happens when you are asleep because when you are awake the muscles in your throat keep your airways open.

When your airways are blocked your brain doesn't get enough oxygen and so it wakes you up just long enough for your airways to open and breathe again. Usually you don't remember but this can happen many times in a night which means you don't get enough sleep.