While Italiano doesn't seem to take your concern seriously, YOU NEED TO.

You need to go to your doctor IMMEDIATELY and tell him/her exactly what is happening. Tell him it happens when you smoke pot (he can't narc on you). No need to feel guilty/ashamed/embarassed disclosing that you use. You are not the first patient to disclose this; it's very common (trust me, I know). Doctors are bound by HIPPA and confidentiality laws, so he don't worry about legal ramifications or anything. The more information your doctor can have about the issue, the better they will be able to help.

Point is, get to the doctor immediately. Blacking out is DANGEROUS. Losing consciousness is even more dangerous. And I mean life-threatening. If you think of your brain like a computer, blacking out is similar to not shutting down your computer properly, and you risk damage (and even the possibility of not "re-booting" correctly). Please go see your doctor. And don't smoke any more until you do.