This came up on a different thread but I thought it might be helpful to many of you that live in the US. These are links to the US Department of Labor.
Here is some information on FMLA (family medical leave act): http://www.dol.gov/esa/whd/fmla/
Here is a link on ADA (American's with disabilities act): http://www.dol.gov/dol/topic/disability/ada.htm - go to the lin on Job Accommodations - that seems especially helpful, including a link to a group that helps people develop accommodations.
The state you live in may have additional protections so you may want to look at your state's department of labor site.
Your employer may have additional programs as well. But at minimum they need to meet these requirements.
I think it is important for eveyone with a health condition to know about this because often employers (managers) don't know or don't share and the employee ends up getting fired when they shouldn't have. Anyway, I hope you find it helpful.