Emergency services responded to reports of concerns for the welfare of a person at the Chatsworth Hotel in The Steyne in Worthing at 9.30am.
An air ambulance was dispatched to the area to take the man to hospital.
Ambulances and a fire engine were also in attendance.
A spokesman for South East Coast Ambulance Service said: “We have responded to reports of concerns for the welfare of a person at the Chatsworth Hotel.
“Ambulance and air ambulance crews have attended and the person has been taken to hospital in a serious condition.”
West Sussex Fire and Rescue Service have been contacted for a statement.
