I had Preston as my companion, and I was engaged in a firefight near some deep water. He got downed so I stimpacked him, but a car exploded as soon as he stood up and sent him flying into the water. Ever since then he has been stuck lying face down on the ground, sliding along it to follow me. Commanding him to go somewhere results in him teleporting to wherever you point (or sometimes closer to you) and he can not use his weapon or move very far in buildings. I have tried reloading, and so far, the only thing that will fix it is reverting to a save from about 30 minutes prior. I can access dialogue with him, but sometimes it gets stuck and you can't exit the dialogue and must reload a save. When trying to dismiss him he just stays there and doesn't move.