Wade, who has battled migraines for years, took part in the team's morning shootaround but starting feeling sick during the day. Usually Wade has issues with light sensitivity when the headaches come on.
"It started to set in this afternoon," Heat coach Erik Spoelstra said. "He really wanted to give it a shot."
Wade has missed 13 games this season, mostly due to knee soreness. The Heat are 7-6 when he does not play.
It was Douglas' first start since being acquired in a trade from the Golden State Warriors last month. He had only played three minutes in three games for the Heat.