Brooks, who has been open about his ongoing battle with anxiety, took to social media Monday to address why he had an early exit against the Seahawks.
"I'd like to address what happened yesterday," Brooks wrote on Twitter. "I woke up, and did my typical routine of morning vomiting. It didn't go away like it normally does, but I figured it would calm down once I got to the stadium. It did, but I felt exhausted.
"The nausea came back, and I tried to battle through it and went out for the first drive. The nausea and vomiting came back until I left the field, and tried everything I could to get back for my teammates but just wasn't able to do it.
"Make no mistake, I'm not ashamed or embarrassed by this nor what I go through daily. I've had this under control for a couple of years, and had a setback yesterday. The only thing I'm upset about is that when my team needed me, I wasn't able to be out there with and for them. Lastly, I appreciate the support of my coaches, teammates and fans. It doesn't go unnoticed."
Brooks has missed five games in his NFL career because of an anxiety-related illness. Before sitting out Sunday's game, his most recent absence came in 2016, when he was forced to miss two games in three weeks.
Without Brooks and right tackle Lane Johnson, who missed Sunday's game because of a concussion, Eagles quarterback Carson Wentz was sacked three times and turned the ball over four times (two interceptions, two fumbles) against the Seahawks. Seattle beat the Eagles 17-9 to remain unbeaten on the road this season.
Brooks, a 2012 third-round pick by the Houston Texans, has emerged as one of the best offensive linemen in the NFL since joining the Eagles in 2016 as a free agent. Philadelphia made him the highest-paid guard in the league after signing him to a four-year contract extension earlier in November.
The Eagles (5-6) will play the Miami Dolphins (2-9) on Sunday.