I believe you were trying to do too much. Try keeping a health journal everyday so you can track what your triggers are. By following activities and symptoms you will discover what your triggers are. Be sure to take a rest break every hour! Even if it is only 5 minutes. While it may be hard to slow down your brain really needs every bit of rest it can get with very low stimulus. Going into a store with bright fluorescent light, advertising at every angle, music blaring and people bustling all around is just way too much stimulus.