By the way, if you never had anxiety attacks until you took the meth, you might not have a chronic problem -- you might just be stuck scared from the bad experience. Did you try therapy before medication? You might be able to get better by understanding what happened and cutting off your thinking from becoming a chronic problem. Therapy works best when you know why you have the problem.
Technically, no, you can't take them both, as almost all of the ingredients of Serelax target GABA -- it even includes GABA, though it's worthless as it doesn't cross the blood/brain barrier very often when taken as a supplement -- and benzos also target GABA. But I wouldn't take this formula anyway, just because it contains things that definitely seldom work, such as GABA, and because it's an internet and drugstore company essentially, meaning they don't probably know how to source the best herbs. But again, if you're taking a benzo, you'd probably better stay clear of this supplement since you don't probably know herbal medicine that well.