For me, it started about 5 ish years ago. Late adult onset. Never as a child. At first it occurred maybe twice a year. Now it happens maybe 10 - 14 times a year. Once it happened two days in a row.
It ONLY happens if I'm dreaming that I'm peeing. BUT if I'm dreaming that I'm peeing,I don't always pee myself. This is how I know, the dream comes first, then I pee myself.
In some dreams I'm thinking something is wrong, and then tell myself in my dream, 'Look down. Its ok to pee. You are sitting on a toilet.' I look down and see that I'm sitting on a toilet and it happens. Sometimes I catch myself and wake up and rush to the bath room.