You can unzip it enough to get your head out and the dino head falls behind you like a hood on a hoodie. The fan still keeps the costume inflated. But if is difficult to sit down with the fan running. You could always just shut off the fan while you are sitting.
How long does an inflatable costume last?
As you'll be able to see in this video, putting on your inflatable costume only takes a minute or so, so no need to stop the (responsible) boozing this Halloween! Just so you're aware, this costume comes with a battery pack (to power the fan) which takes 4 AA batteries and should last around 4 hours.