Kubiak suffered a mini-stroke, also known as a transient ischemic attack, during halftime of a Texans' game in November. The ailment caused him to miss several weeks and limit his work hours initially upon his return.
Kubiak, 52, said he was working full-speed when he was fired by the Texans with three games remaining.
The team finished with a league-worst 2-14 record during the regular season.
"I went through about a three-week process where I cut back my hours a little bit," Kubiak said. "I came out of it fine. I was my old self at the end of the season. But things didn't work out, and that's part of this game."