It does happen during some astral projections either on leaving the physical body or on trying to get back into it, that one goes into the sleep paralysis and then slips out of that and then is pulled back into that once, twice or more times. It feels very unnatural and uncomfortable. Always be sure that your physical body is getting fresh air, since if it is breathing stale air, it might cause the astral body to have difficulty synchronizing. Don't just rely on a duct system, try to have a pin crack at a window for direct air from the outside if possible.
But don't confuse the lack of synchronization of the two bodies with a bad experience which happen at the same time. In other words, if someone comes there and scares you while that is happening, the two factors of the lack of synchronization and the scaring are actually separate.
Like if you go up to your door at night and then a robber appears there. The night time and the robber are actually two separate issues, even though the robber would take advantage of the darkness of the night.