I'll first tell you the dream, then the circumstances, then the reason I have it, and believe me, it's a headache (literally).

I'm in a room on the wall (like a bug), and the room is all smooth and seems impossibly expansive. The room is all quiet, but suddenly it contracts and becomes unimaginably rough and loud and small—then back out quiet smooth and going on forever. In and out and in and out until I wake up.

It's very painful, when it's loud, and here's why. Every time I have this dream I'm very sick with a migraine. It's the migraine that's important here. When one has a migraine, every heart-beat is painful. Anyone who's had one will know exactly what I'm talking about. Now, the reason why I have the dream is the migraine itself. The pulsing of the blood is the in and out, the in being the hard attack when the heart beats and the out being the lull in between the heartbeats. Not a very pleasant dream to be honest, so I'm very glad I haven't been sleeping with a migraine in a long time.