There's no such thing as a "normal 10ft east coast wave, they are far and few between, but to answer your question, yes you need to be prepared for that, going out once a month isn't going to get it done, so surfing as frequently as possible and slowly pushing your limits higher and higher will eventually get you there. I've managed to pick a few 8 footers off here in FL, 10 foot I've maybe possibly gotten in PR, but i'd be willing to be it was closer to 8 than 10, but they all felt like 10 foot that day, so much different down there than here. Do you need to train to the level of a pro? No, but you want to be in good shape, and can hold your breath for a good 30 seconds at least, maybe longer depending on how long the period is between the next bomb that's going to break on your head after coming back up gasping for air...
If you have to ask you can't handle it. Sorry if that sounds rude but it is the truth. A 10 ft wave on 90% of east coast beaches would mean closeout city and you would never make it past the shorebreak wall of whitewater. But just to give you some perspective during one cane swell 2 years ago (don;t remeber the name) it was like 6-7 ft so a foot or so overhead. I got held under for what to me seemed like an hour. When I surfaced my buddy told me I was under for at least 1 -1 1/2 minuets. While that may not sound like long try holding your breath for 90 seconds while sitting at your desk reading this forum. If you can do that next try and hold it for 90 seconds while doing cartwheels and push ups and see how it goes. Unless you are ready to for that stay on the shore.
Dude, as long as you don't smoke Marlboro's and drink Kasser's vodka daily, you should be ok if you are in normal shape.
If you are young and excercise-minded, it all boils down to mental state.
If you have fear and are worried than you panic which releases all of your air in your lungs.
Getting to a zen mental state isn't easy, but doing cardio exercises will give you confidence. Shoot, I'm still wary on the bigger stuff as it closes-out three feet in front of me. Part of it's because I don't use the leash and a part of it is because my mind is wacky because I used to smoke and sh!t. Part of my mind still thinks my lungs are black and tarred. The mind is a strange thing. Plus, I'm kind of over paddling out into big garbage and chasing a corner around for forty minutes.......Big waves around here are garbage.......
Get in good cardio shape and then train your mind to relax. Watch an overhead wave break. Watch how quick the white water disapates. It's not that long. 10 seconds - tops. Yes, time seems longer when you're being worked, but it's all mind over matter. Easier said than done, but that's what it's all aboot.
You ain't going to be held under for 90 seconds. Not on the east coast and not even at Mavericks(Rarely). People have been held under for two 25 foot waves and popped-up in less than a minute.