Abscess? half rotten back left upper molar tooth that doesn't hurt much but get headaches and anxiety? the gum is swollen in very back?! scared!

Would recommend : Not procrastinating and go to see a dentist soon before the condition gets worse. Don't be scared - waiting will only make it worse.

Check w/ dentist: A dentist will be able to examine your teeth and determine if there are stress cracks that may be caused by grinding teeth (a common symptom of anxiety) and can lead to tooth decay. Headaches can also result from stress grinding. If necessary, you can be fitted with a special mouth guard to reduce some of the symptoms resulting from grinding of teeth. A psychotherapist may be a good follow-up.

Rotten Tooth: You most likely have an abscess, especially if you are swollen. Pain not the issue here, but ignoring the problem is. Why wait? Call a local dentist and have the tooth evaluated for restoration or extraction. The pain may start suddenly and may be severe. Infection can spread, too.