Yes, same here - i get dehydrated after riding as I forget to drink enough (p goes very dark ... too much info?). I really must try harder to drink more, and not just beer or G&TI sometimes get dizzy when standing from a seated position, but not from lying down.
It’s been better over the last year, as I’ve tried to pay more attention to staying hydrated. I’ve always struggled to drink enough when riding and have tried much harder to drink when riding and after riding. It does seem to have helped.