PSA to check your hot water bottles for leaks. I got into a wet bed last night and realised mine had wet itself. Thankfully I actually didn't refill it last night so it was left from the previous night and must have just seeped through some very minor crack in the rubber.
I'm always super careful with making sure the lid is on tight because I knew someone who had their back burnt due to a leak. I just didn't really think the rubber itself would wear away but to be fair I've had mine for quite a few years. I just took a closer look and can see there is a tiny hole near the neck of the bottle which is presumably where the leak is coming from.
I think you are supposed to get a new one every 2 years? The rubber degrades from the heat and becomes stiffer and therefore more prone to cracking or bursting.