system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that when walking home I moderately have to pee, but upon reaching the door and stepping inside it feels like I'm about to piss myself?
gpt
This will be an example of trained reflexes in your body. If you are out and about there is not going to be a toilet anywhere, so you're not in the situation you'd usually be in if you were to pee. Your brain registers this on a subconscious level and tells your body "don't piss right now". Obviously you have to piss eventually, so your bladder will let your brain know that it's pissing time and you'll feel a little need to pee. 

When you get closer to a piss destination your body will be all like "hey yo it's pissing time let's do it" and start prepping your peehole for pee pee, thus the need to piss gets bigger. It's just you associating home with being able to piss that makes it seem more urgent.