In general, I think the two main benefits that can come from a formal diagnosis are:
- access to services and/or treatment
- possible legal protection under the Equity Act
Speaking from my personal experience with autism/aspergers, diagnosis meant I could access an aspergers-specific service at the local mental health trust, which has meant I have someone there who knows me and understands because they are a specialist and I can access help from them quite easily (I have their direct number and they usually get back to me within a day). Also they run various groups, of which I attend a reading/social group which is some months my only social activity at all.
Depending on your possible condition, your level of need and what is actually available locally, access to services may or may not be relevant.
As far as equality act stuff goes, with a formal diagnosis you would be entitled to reasonable adjustments at work (and supposedly with public services, but pretty sure that latter only really gets paid attention to with straightforward access stuff) if you need them. You might think this is irrelevant, and it could be for you currently, but bear in mind that situations like that can change quite quickly through a variety of things you might not even anticipate, and if you already have the diagnosis then you won’t have any delay on that end of things to ask for adjustments.
Another thing as well is, there is no reason why you would have to disclose a diagnosis to anyone you didn’t want to (until such time as you might need to, such as seeking adjustments at work), you could just keep it to your partner or maybe close family or friends you really trust if that was all you wanted.
Do you know what it is about the prospect of the diagnosis that upsets you? (don’t feel you need to answer that if you don’t know or don’t feel comfortable)
It seems, like @he_2 touched on, that it is a good thing if you have ideas to try out things you think could be beneficial whether or not you seek diagnosis. I hope you find things that help x