Should i be worried that i feel lightheaded and have headaches after going to the dentist?

Depends: If the symptoms last for only a short period of time, there is probably nothing to be concerned about. If they are persistant, you should consult with your doctor.

Yes ish: Have your blood pressure checked, a condition called orthostatic hypotension exists and commonly causes fainting, or dizziness/lightheadedness after being in the chair if you have a pre existing condition. This may be serious so see your physician.