It's just an annoyance. For PMS I get a mild backache, fatigue and uh, a minor digestive issue. My period only lasts 3 days.
The fatigue is sometimes bad enough to interfere. I know if I take vitamins it can help, but I'm really bad remembering that kind of stuff.
On a funny note, I once had a nurse argue with me about my periods. She said I was lying because the average period lasts 5-7 days. I defined the word average for her, she didn't appreciate it. that woman was weird. She was just taking my medical history and she kept arguing with me about it. It was odd.