If it's really debilitating then I take a sick day. This is done through an app so I don't need to justify it. The only time I tell my boss is if it hits in the middle of the day and I need to stop working, which usually doesn't happen as I can usually tell when I wake up whether it's that bad or not.
I'm fortunate enough to work from home so it's nice that I can do whatever I need to get me through the day, like if I get nauseous I can puke freely and carry on without worrying about anyone hearing or walking through the office looking like garbage.
Mine are not that frequent though, at worst it's like once a month. I have a friend who has it really bad, she's been off work for ages because anything can set it off but she has no idea what, or how to get relief.