Suddenly switching sleeping locations? My betta used to consistently sleep on the gravel.  When I got back from a week-long vacation, he seemed a little listless, though he looks better now.  Then and since, though, he's been sleeping on the roof his castle instead, or inside it.  I know it sounds a little crazy, but could he be doing this because he's sick somehow?  He seems like he has been a little slow lately.  Usually he flares at and chases his reflection a lot, but lately he's been swimming around pretty slowly.

The water temperature is between 68 and 72, usually around 70.  I have a heater, but it's not doing much to combat how cold my dorm room is so I'm not really sure what to do about that.  I also don't think I found all of the remnants of the live plants I had that ended up rotting recently, so maybe it is issues from that?