Manager Charles Lago told several media outlets that Sizemore was discovered at his home at around 2 AM and transported to the hospital.
Sizemore, age 61, is “under observation,” Lago said. “It is too early to know about [a] recovery situation as he is in critical condition under observation.”
The actor’s resume includes the films Black Hawk Down, Born on the Fourth of July, Natural Born Killers and Heat.
Next month, he is starring in science fiction film Impuratus, in which he plays a police detective who is forced to believe in the supernatural after witnessing a Civil War veteran’s death bed confession.