Before the first verified individual migrating birds in the 1800s (via finding storks with spears still in them after migrating to and from Africa) people had a lot of weird ideas about why birds weren’t there in the winter. “They fly so far it’s literally off any map you’ve seen” probably made as much sense to the average person as them flying to the moon, or burrowing into the mud at the bottom of ponds to hibernate.
The latter probably made the most sense to many people who lived rurally, because bank swallows (sand martins elsewhere) actually do nest in tunnels they’ve dug into the sand near bodies of water. To anyone who went without seeing one all winter and then suddenly saw one leaving a burrow in the spring, ‘it slept there all winter’ is a lot less of a leap than ‘it flew thousands of miles round trip and got back when you weren’t looking.’
My mom was bipolar, but since she grew up in the 60s and 70s her experience probably isn’t going to match your son’s much. Especially since she didn’t even get a diagnosis until her mid/late 20s, after having symptoms for years.
So, the not sugar coated version of what I experienced: she was a drug addict, alcoholic, and would alternate between abuse and neglect. I’m sure part of that was no/wrong meds for a while, plus it culturally just being more okay to smack your kids back then. I saw a lot of screaming and arguing and crying that I thought was normal. She and my dad lost custody of one of my siblings for a while.
So that’s what poorly treated bipolar disorder can look like. That’s the bad place it can go if he decides he doesn’t need his meds anymore and there’s nothing wrong with him, which is made worse by the fact the meds are supposed to make you feel ‘normal,’ and some people prefer the mania to ‘normal.’
It’s absolutely manageable for many people, especially if he stays on top of his meds. It may not mean that he never has symptoms or that they don’t change, or that they never temporarily get worse or better. If he isn’t already in therapy that’s something you should really encourage, because meds are just one tool in the box, not the whole set. You mention a psychiatrist, but they manage meds rather than the emotional aspect, and it’s important to see a psychologist or therapist at least for a while on top of that.