Do you feel like you need to disclose, or can you turn in your notice for "personal reasons" or seeking a different kind of employment? I would struggle with disclosing, and if you're leaving anyway, my personal belief is that no one at the job is entitled to know. I'm sorry I can't offer any advice if you do want to disclose.

if you don't want to disclose, what I have done in the past is informed my employer that I was leaving for personal reasons, that I had things going on in my personal life (you can specify that they're medical reasons but you dont have to) that were making it difficult to keep working and that i needed to take a step back. if they try to press you for a deeper reason why, remember that "no" is a complete sentence! they arent entitled to that information, and you dont have to share anything you dont want to. "that's personal and i dont want to talk about it" is a good way to shoo them off. i have a tendency to heavily script things (from a two week's notice to normal everyday interactions), so if you need help writing something out then youre welcome to message me!

Ya know, maybe people might respond supportively to you if you just let them know. The climate is progressing for those with mental health disparities and I would think they might even accommodate to your needs. At the very least, you might even be able to find alternate work at the company, something that works out for you and your employer. Just don't shut yourself down, look at how hard you worked to get where you're at.