This has happened to me a few times before, and in the last lucid I had as well. I’m having just the regular dream when I realize I’m dreaming, but as soon as I do I am paralyzed. I fall to the ground and can’t move… I think of things to do, such as spin (to teleport) or verbal commands, but since my body can’t move (Including my mouth) I can’t do either. It’s bothersome cause all the times, except for once that i can remember, i wasn’t able to get out of it and just woke up.
what to do? what to do? has this happened to anyone else before? 
, i’ll try what you said. i’ll try to stay calm, and breathing deeply is a good way to do it.