As Cane2theLeft stated is is not possible to determine what "too much" Ativan is. Based on many factors such as genetics/natural tolerance and developed tolerance, etc., how much one can handle varies from person to person. You also mentioned that you were drunk, although you didn't include how much you had to drink or how much alcohol you can handle.
And there is no need to worry I doubt you had a heart attack, but rather you misinterpreted what the doctor told you. Consuming too many CNS depressants will cause your breathing to slow and become shallow until your heart stops. So I think the doctor meant that you are lucky that you woke up after such a heavy consumption. Although Ativan is a weaker benzo, 35mg is a lot to consume if you do not have a tolerance. Especially when you were also drinking - and I assume you had quite a bit to drink as you said that you were "hammered."
Like others have said, benzos alone are very hard to overdose on (you'd pass out before you had the chance to take enough to kill you) but mixing them with alcohol or other CNS depressants is like playing with fire. A little bit of each goes a long way. You really are lucky that you were completely fine. Just be careful in the future and learn your tolerance before you use high doses like that. For harm reductions sake please do not mix drugs like that unless you know what you are doing. I am sure that you didn't have a heart attack or any damage or problems elsewhere (the doctor would have mentioned it obviously).
Seriously though, you are lucky because many horrible things can happen when you take so many depressants even if you don't overdose. You could choke on your vomit, if your breathing slows enough your organs could begin to fail from a lack of oxygen, among many other things.
I am an example. I overdosed on oxycontin about a year ago. I thought I knew what I was doing and that I was an experienced drug user, although I was somewhat new to opiates. I fell in love with them so quickly and began using very often right off the bat. One night I was doing oxycontin and coke. The coke made me so up that I kept snorting more oxycontin to get a good "balanced" speedball. Like an idiot I didn't pay attention to how much I was doing. I felt fine so eventually I put myself to bed. As the coke wore off I drifted more and more into sleep. My friend did not wake up and find me until 12 hours later. My liver, kidneys and pancreas had failed. I WAS DEAD, give it another 30 mins.
Well anyway, I'm a lucky son of a bitch because my organs returned to full functionality in a few weeks. However, because I was passed out lying motionless on my right shoulder/arm with no oxygen to it for so long, I had severe nerve compression damage. My entire right arm was initially completely paralyzed for a few days. Then I suddenly gained enough functionality to move it around a bit, although it was still mostly paralyzed in the sense that I couldn't move it - only certain parts were actually numb.
It has been an extremely slow and stressful process but it is healing which is just amazing. for months it stayed the same and wasn't healing. Now I can finally write and I can pick most things up, although the nerve running up the pinkie is still numb. and the pain is GOD AWFUL. Ironically now I'm prescribed opiates because I just can't take the pain.
SORRY this is so long, but I just wanted to make a point. Be careful taking large doses like that when you are drunk. Don't do a ridiculous thing and THEN get on bluelight and ask if it was okay, but rather ask here first to see if its a good idea or not. I'm just saying people think they are invincible and its not going to happen to them but shit really does happen. I put my fucking self to sleep and still overdosed. And now I have this pain ridden nerve damaged arm and I'm right handed. FML hah.
