That happens a lot when the body is stressed. There might not even be a feeling of stress but its still important to fully relax before sleep. This is something I have trouble with and have been working on. It usually works very well if I can maintain a strong intention to remain relaxed. Focus on your breathing and try to feel the relaxation consciously.

Going into Sleep Paralysis(SP) is a good thing. It gives you more experience and lays out a general idea of what you will encounter later. Once you are able to relax, you may find you fall asleep too quickly, so there is always a balance to be mindful of as well.

keep up the awesomeness!