Jackson had missed the past two days of practice because of a non-COVID-19-related illness. On Friday, he participated in all the drills during the media viewing portion of practice.
"[I feel] way better than I was a couple of days ago," Jackson said with a big smile after Friday's practice. "I'm feeling great."
Jackson said he was dealing with a cold. He has now missed four practices this season because he was sick, and he has been sidelined for at least one practice in each of his first three seasons because of illness.
Asked why he gets sick so often, Jackson blamed it on the change in weather.
"I usually don't get sick, for real," Jackson said. "I used to eat my Flintstone vitamins when I was a kid. My immunity system should be good."
Jackson has missed at least one practice in four of 11 weeks in the regular season this season. His latest absences came after the Ravens were held to the fewest points with him as a starter in a 22-10 loss at the Miami Dolphins.
Jackson estimated that he's 2% behind his teammates after being out for a couple of practices this week, saying the missed time can affect chemistry with his receivers. Ravens coach John Harbaugh said it's "not ideal" for any player to be sidelined for practice.
"Practice is very important," Harbaugh said. "That's how you get good at what you're doing. That's how you get things oiled up. So, it's factor."
Jackson leads the Ravens and the NFL's No. 2 offense into Chicago, where he will play the Bears for the first time. His 25-2 record in his first start against teams is the best by any quarterback since 1950.