First of all, tricyclic antidepressant overdose is both slow and painful. There is no such thing as 'falling into a coma' peacefully, although your mind may wish to go your body will
fight for life - and that's a process that is far from pleasant. If you do overdose, please don't use these.
Regardless, what is it that make you want to die? Are you in physical pain? There are countless drugs out there that can help alleviate this, and your doctor would no doubt do everything they can to help.
Before you do anything, please take a read of
this, and know that your pain is only temporary. If anything, you can survive another day so wait until tomorrow. If you have everything to loose, why waste time now suffering. Do what you can to get through today, and ignore the consequences.
Best of luck

And please talk to us so we can help you, the very fact you made this post shows that there is part of you that wants to live
EDIT: Just saw your recent post, what is it that you're suffering from, if you don't mind me asking?