Unless I'm tilting I usually stop looking so hard for 3bet spots and play a lil tighter. It's just a matter of your brain being overworked and not focusing as much. There was some good discussion about it toward the end of
this thread if you want to check it out sometime. Basically your brain is most focused only 30 min at a time or something like that. So it's normal for someone to go into "auto-pilot".