Has anyone else had problems with their employer and ADA?

Problems with Employer/ADA? Please help!!

Hi there, I'm reaching out on behalf of my fiancee, who I believe is being treated unfairly at his workplace. He is 24 and suffers from severe arthritis (diagnosed at age 17) and currently does not have any ADA accommodations, as he doesn't require any specific accommodations for his position. Recently, he's had to leave work or be absent from work (not often, just occasionally) because his medications made him ill, and they are starting to give him a hard time. Today, he was told that he couldn't leave even though he was throwing up in the bathroom--he had asked to leave early and take the remainder of the day (4 hours) off and use his accrued PTO to make up for the difference. They said 'seemed odd' since we are heading into a long weekend, and implied that he was trying to leave early for his own benefit. They then sat him down with HR and mandated that if he does not get the ADA Accommodation form filled out, they will take 'disciplinary action' and write him up formally. To me, this doesn't seem ethical or legal--yes, his condition is the root cause of why he is feeling ill, but no other employee is being questioned for leaving early when getting sick. Ultimately, he wanted to avoid the ADA Accommodation simply because he wants to be treated the same as anyone else, he's not asking for any differential treatment. I just want to know if there is any recourse we can take? It absolutely kills me to not only see him in so much pain, but now dealing with this! Any advice or input is greatly appreciated, as he is worried about being targeted for this and potentially losing his job. Thank you!