I'm having this issue where a few hours after I fall asleep, I wake up with shortness of breath. It's really alarming because it happens out of nowhere, and I don't know what's causing it. After I drink some water, I feel better, but it's unsettling not to know why it's happening. There's no chest pain or anything like sweating, just this sudden breathlessness. Can you help me figure out what might be going on?