I am being served with divorce papers claiming I have a mental illness. I have never been diagnosed... can my husband do this?

Your husband and his attorney cannot file false pleadings. If there is no evidence of a mental illness and they put that in a signed pleading with the court they can be sanctioned.

You'll see all sorts of creative pleadings in the Domestic Relations division. If it's solely related to showing grounds, I'm not certain the judge will care; grounds has no impact on property division and maintenance. Also pleadings can be amended, so perhaps they'll agree to I/R w/6 month waiver or some other mutual acceptable arrangement. HOWEVER, if it's related the custody/parenting time or an allegation of dissipation, then different story - and I agree that if it's a misstatement of facts, then you need to throw down the gauntlet and deal with it. Talk to a family law attorney in your area for specific guidance.

most likely it says that you have been guilty of extreme and repeated mental cruelty which is one of the legal reasons to end a marriage. take the papers to a lawyer for advice when you get them.