The reason we say to avoid movement is so that your body can “fall asleep” or go into SP faster. If you move without thinking, you’ll prolong the process but it won’t ruin it. The thing that ruins it is thinking “CAN’T MOVE… CAN’T SWALLOW… MUST NOT MOVE!!!”
If you have an itch, or you’re uncomfortable, or you need to swallow, fix it! Just don’t devote a lot of thought to it. Do it naturally like you do when you’re awake.
Now, once you’re in a comfortable position you should try to ignore what we call “roll over signals.” They are a way for your SC to test whether you are awake or not. If you don’t roll over, your body will fall asleep faster so you don’t have to keep your mind aware as long. The longer you make it, the more difficult it can become.
All of this varies from person to person, so it is important for yu to experiment some and see what works best for you