You have to work up to it. It takes getting used to the device. I sometimes have trouble falling asleep, and when I do, I take a couple of Tylenol, to take the edge off, and I usually fall asleep after that.
There is always going to be that 2 am wakeup, where you are trying to erect, but the device is stopping that, Get up, go pee, and back to bed.
It will take a while to get used to sleeping in it. Try half a night, or taking a nap.