How could you forget to do that (unless you have a medical issue which genuinely makes you forget to stay hydrated/not feel thirst or something like that)?

One such disorder would be ADHD. ADHD has a lot more symptoms than people think. Sure, you’ve got the rambling speech/jumping topics/high speed talking but there is far more than that. One thing is that when we actually get into a ‘zone’, it’s way deeper than a neurotypical gets. It’s a pure fixation that’s known as a ‘hyperfixation’. When in this state the brain will start to dump important tasks to go after what you’re on. The most common task that gets dumped is basic bodily care. You won’t drink water, you’ll neglect eating, and you’ll often try to avoid using the bathroom by holding it until the last possible moment. You just don’t want to stop doing what you’re doing.

However even when not fixating the brain will still often dump that task. If you’re in a particularly ‘manic’ state, or more of an active state, you’ll just forget to drink water or to eat. It’s just not classified as something important to do. Example? I’m typing this out to you while only now realizing that the last time I drank any water was when I posted this comic strip 12 hours ago. Am I thirsty? Yes. My mouth is actually a little dry and it’s kind of uncomfortable. But I genuinely was forgetting that I needed to drink water.

ADHD is horrible.