"Kony 2012" details the atrocities committed by Ugandan warlord Joseph Kony. The video, produced by the charity group Invisible Children, became an Internet sensation this month. Russell is the co-founder of Invisible Children.
Authorities say Russell was detained by San Diego police and hospitalized after running through the streets in his underwear, screaming, yelling and interfering with traffic on Thursday.
After police interviewed him, they decided that he needed medical attention.
Invisible Children CEO Ben Keesey says Russell was hospitalized for exhaustion, dehydration and malnutrition. He said recent severe emotional toll manifested itself in "an unfortunate" incident, but did not offer any further details.
The Associated Press contributed to this report.