First question: Is it normal? No. Most people do VO2max intervals in the saddle.
Second question: Should I decrease the power?
Probably, yes, but it depends on your goal. If all you’re trying to do is replicate time under tension in a race condition then gawn & get up out of the saddle. It’s what you’d do in a race anyhow.
If you’re just trying to collect minutes at a VO2max condition it’s probably better to lower the power and remain seated. You’ll be able to crank out more intervals that way, probably.