Conaway, 59, fell down a staircase and suffered a broken hip, a broken arm, a fractured neck and a brain hemorrhage, according to TMZ.com, based on information from his girlfriend, Vikki Lizzi.
He was rushed to hospital for surgery. No other details are currently available.
Conaway has battled substance-abuse problems throughout his life. He appeared on Celebrity Fit Club in 2006, but had to leave due to a drug relapse.
He later appeared on two seasons of Celebrity Rehab with Dr. Drew.