I don't think one needs to disclose to their employer unless they they themselve anticipate it being a problem.

I don't know if she has been diagnosed but my 28yr old daughter has a great deal of difficulty. She has real problems with the period itself, becoming near incapacitated 2 days out of every month.

She does exibit changes to her behaviour but I wonder if it is more irritation and anger at knowing what is coming up. Not sure. I've never thought until now it might actually be a diagnosible problem.