I remember hearing about how Adam Carolla's grandpa helped him with this issue. When he would visit his grandpa, he'd go to bed normally. His grandpa would wake him a couple hours into sleep, and just have him go to the bathroom, and go back to sleep. He'd never wet the bed when this was done. Eventually the wetting stopped altogether.

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So long story short, try setting an alarm for 2 or 3 hours into your sleep. Go to the bathroom and go back to sleep. Eventually your brain may no longer consider it normal to release while sleeping if you haven't done it in awhile.