Ouch.
Yep, something none of us want or need. A Viral Illness, all that to add to our already challenged system.
Dehydration is a worry for sure. Even if you have to use things like Pedialyte, or Pediasure - keep up the fluids and supplementation plus water; lots of water.
When sick with the flu, whether stomach or respiratory we are losing fluids with everything we do - breathing, bathroom, sweats, everything - at a faster rate than usual. Our bodies are in high gear working to expell the offensive microbial infestations causing our illness, making antibodies, taking everything it needs from our reserves to assure it can win that internal battle.
Get well , Best wishes, Feed a cold, Starve a fever, always give your body fluids when sick.