Sometimes when I'm at a red light with the brake held down, the brakes on the car release for like a second that grip really hard. Kinda feels like someone hit me from behind, but its really just the brakes. Is this normal?

 

Weird..funny how you mention this now, I have a 2008 IS250 and it did that to me today for the first time, I thought my foot twitched or something but I know it didn't. I'm sure it's normal..if anything it's the BRAKE ASSIST acting up