What will a overdose of sleeping pills do?

I can only speak to what my experience is. I overdosed on more than 50 otc sleeping pills and consequently spent 3 days in a coma. Ever since I've had short term memory problems and deal with being tongue tied every now and then. Basically it feels like a decrease in the level of activity my brain is able to do. Although, since I was in a coma I'm not positive if all these side effects are strictly from the OD or the coma.