My boyfriend Spits in his sleep.

How do I stop this? He’s always been a sleep talker, usually repeating conversations he’s had throughout the day or sitting up to look around the room as if he’s never been here before. But a few months ago was the first time he spat in his sleep… I’m talking HAWK TUAH in the air and landing next to him or directly back onto his face. It’s disgusting but he genuinely can’t help it and doesn’t even know that he’s doing it unless I tell him the next day. I’ve searched up everything I can and the only thing I could think of is that when he clears his throat in the car he spits it out the window constantly. Could it be a form of sleep talking?… sleepspitting? Is there a way to stop it? I’m tired of washing pillowcases everyday and I’m tired of keeping an eye out in case one lands on me. Pls help