Beer causes intense heartbeat

About a year ago I started drinking fairly heavily.. and for a long time it had no side effects other than a hangover.. but latley it seems that when i had 8-10 beers i wake up a few hours after going to sleep with a very fast and very intense throbbing heart beat. it scares me but im usually still drunk so i just forget about it and go back to sleep.

Last night i had about 10 beers came home and went to bed shortly after, i was still very drunk... i woke up after about 3 hours of sleep with my heart beating so deep the sound of it actually woke me up, i also kind of felt like a vibrating or muscle contraction in the left upper back but i went back to sleep. now ive been up for about an hour and my heart rate has slowed right down, its back at about 70ish, which is normal for me.. but i feel light headed and a bit weak. i also had a very salty meal before i went to bed.. that could be a big factor.