lol... but seriously, we deal with them in a way that you rarely, if ever, notice. Depending on the severity, some people might take time off ranging from a day to a week and they are able to predict that because we've been taught from an early age how to track. Nowadays apps make it easier to track. In regards to arousal... you'll need to ask your companion of choice.

She is a long-time regular.  She was having a great time right along with me, both of us O'd and then we discovered she'd started her period.  She was totally embarrased, but no big deal to me; it's just nature.  She explained that she'd started a new birth control method (we always covered up, of course) which she felt was why she was caught off guard.  She did say she felt very turned-on, and I've been with other women in my life who said the same thing about period sex.  Try it if you ever get the chance.