Wait till standing desks have been in fashion for some decades and you'll start seeing stories about people getting Thrombophlebitis in their legs.

Seriously, get a good chair and sit in it. Get up every half an hour or so, also strech your legs while sitting. Raise your toes forcefully to get some blood flowing through your lower legs (this should be done automatically every couple of minutes without thinking). Put your feet on the desk every now and then.

Do some rigorous exercise every couple of hours or so.

And you should be fine.