Can someone suddenly develop ADHD as an adult with no childhood history?

Adding the mildly annoying but necessary caveat — 'ADHD' has become a bit of a default explanation for burnout right now, so it's worth making sure whoever assesses you is actually doing a real differential and not just pattern-matching your symptom list to a diagnosis because it's the one everyone's talking about lately. Doesn't mean it's wrong for you, just make sure the process is thorough.

So the honest answer here, and I say this as someone who went through almost this exact scenario, is that 'no childhood history at all' is worth taking seriously as a reason to look closer before assuming ADHD, not dismiss it — but it's also worth knowing that 'no history according to what anyone noticed' and 'no history at all' aren't always the same thing. I was also the easy, good-grades kid, zero teacher complaints ever. What came out in my assessment was that I'd developed really strong compensatory habits early — over-preparing, rigid routines, using anxiety as a functional (if exhausting) organizing system — that worked fine until my life got complicated enough that they stopped being sustainable. From the outside that looks like 'always fine, then suddenly not,' but the underlying pattern had actually been there the whole time, just invisible because it wasn't causing visible problems yet. That's genuinely different from what you're describing sounding like, and a proper assessment should be able to tell the difference — it'll dig into things like whether you had any subtler signs (over-reliance on last-minute deadline pressure to get things done, needing more external structure than peers even if you always delivered, that kind of thing) versus a story that's really just 'this is new, full stop.' If it really is fully new with zero earlier pattern even under a detailed look, that's worth flagging to whoever assesses you, because you're right that it doesn't fit the standard ADHD picture and they should be actively considering other explanations (thyroid, sleep disorders, depression, just genuinely unsustainable circumstances) rather than defaulting to ADHD because it's the trendy answer right now.