uremia (high blood urea) can give you a painless death, but then you have to have a Kidney problem.
You could inject yourself with fairly high doses of Insulin intravenously and then death comes with a certain dizziness and giddiness and then , that is it! You are far and away! Even Post mortem exam can never prove this. This is the the most favourite method of certain European Nurses to kill patients.
OK, You want to have fun while you want to die! Take as many tablets of Diazepam as you can and then get drunk with your favourite alcohol. You wont even know you are dying.
Medically speaking, there are any number of ways to make sure that patients with terminal cancer die without pain. Epidural injections of Narcotics, individual nerve ablation techniques with alcohol or phenol.
If you have a serious problem , please contact an anaesthesiologist who is near by and is trained in the therapy of chronic pain or a hospice center.
This is not a recommendation for suicide or murder.
I assume a physical pain and not suicidal tendencies.
Source:
Is there any ways to die painlessly? - Yahoo! Answers India