I work with almost all men, so I shared as few details as possible. I basically just said something along the lines of, I have a chronic condition that causes painful flare ups for me and I let them know I was going to PT to manage it. I think that helped them realize that I’m dealing with something and I’m just trying to do the best I can some days.

I work in a Unionized environment and am always in contact with the Union when I am concerned about too many sick days. Based on Privacy laws, my employer cannot ask me any personal medical questions but because my Manager is awesome and is an advocate for mental health, I've shared with her about my Endo and some other medical conditions and she's been super. OK with me working from home, taking sick days, and also suggested considering medical leave.
Sharing is really a personal choice. You don't have to if you don't want to. If your work requires documentation, it could be a simple letter from your Doc outlining symptoms and why you can't be working. I would say to check in with your HR if you have one. Sending you big hugs and hope you feel better soon 🥰

I take a slightly different approach than other repliers here. I like to be really open and honest with them, I've told my employers the symptoms I face on a daily basis - how else can they sympathise without understanding the extent of what I'm going through? Sometimes just saying you have endometriosis isn't enough, it's still seen as being just a 'bad period' by lot's of people.

Endometriosis isn't anything to be embarrassed or ashamed about and you should be able to speak openly about it without feeling like that. I'd request a meeting with your manager to open up a conversation about your struggles, if they're a good employer like mine they should be supportive and offer guidance. My employer allows me to work from home on flare up days, they've also helped me find specialists etc. If you're struggling to work full time, you also have the right to request a change of hours due to medical issues - it doesn't have to be a permanent change, sometimes just 1 extra day off a week can make a huge difference.

Obviously not everyone feels comfortable being so open, but I personally think it's a really good thing if you can be. I see it as my way of raising awareness and removing some of the stigma that comes with womens health

Luckily my current manager understands from similar personal experience but another manager (also female) totally dismissed the severity of my situation. Depending on your employment structure & how comfortable you feel disclosing your condition, share minimal details but be honest about the chronic & how it impacts your capabilities at times. Best wishes.