HIPPA applies to health care providers, not to anyone outside of the system. If your boss had asked your Doc what was wrong with you and the doc then told him...that would have been a HIPPA violation on the doc's part.

Unfortunately in the USA especially if there is no union....an employer can let you go for any reason at any time. Now if your employer fired you because of being too old, disabled, etc etc that would have been a big nono.

I'm sorry this happened to you, the old boss is a jerk.