Classy as fuck . <| sep |> It ' s surprising to see so many varied answers looks like this is just one of those things we don ' t really know for sure , because I have an answer I haven ' t seen here yet . Source close family member had bedwetting issues , and this was from my family doctor . At night we produce a chemical in our bladders that concentrate our urine to a manageable level when we wake up that chemical gets used and that ' s why we usually have to pee when we wake up it was always there , but it had ' t ' overflowed ' yet , so to speak . It explains why sometimes it takes a few minutes before you have to go , but it ' s almost always a part of your morning routine . routine is also likely a part of it as someone else mentioned , it ' s a kind of muscle memorySometimes and in this specific case for my fam the body doesn ' t produce that chemical , and it ' s a bit of a gamble whether or not the bladder will hit its limit during the night in the case that it does , the chemical then also plays a role in waking you up , but in the case where you don ' t have that chemical , those impulses to wake up and hit the toilet simply don ' t happen , and we get a wet bed .