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.
Have you been to see a specialist about it? My friend did, and made some changes to her lifestyle which helped a bit but they're not gone, just better managed.