It’s a common feeling resulting from the sleep paralysis. Some people describe feeling like they are being suffocated (which of course they aren’t).
During the time of semi-consciousness, the cerebral cortex is still half in REM sleep so feelings that are real become mixed up with feelings induced from dreaming. Some people even partially open their eyes to see an arm they thought they were moving laying perfectly still. It’s an odd experience and one I have experienced myself several times in my life since I was a teenager.
The trick is to remind yourself that it’s just part of the dream state and let your body come out of it naturally without fighting it. While sometimes it seems like it’s a long experience, in reality it only lasts a few seconds. Fighting it just makes it seem like it lasts longer that it actually does.