Employee Returning from FMLA

Hi all - I could really use some perspective or your advice. I am returning from FMLA but not back at full hours as I'm still recovering from a medical issue that could last another year. I am doing my best to take care of my health and communicate everything to HR and my manager. I have been with this very corporate company for 8 years and had great performance review but since I have taken FMLA, my manager has treated me with hostility until HR stepped in and now it's very subtle but still there and he has questioned the seriousness of my medical condition even though I have doctor's notes from every visit, he still wants to know more and asks questions even my doctor can't answer because everyone is different.

I was blind to how toxic the environment was but now I see it clearly. How should a person have been treated when returning from FMLA leave and trying their best to get back to full time? Is it normal for managers to be so aggressive and disrespectful upon employees' return?