You won't be able to relax period until you've finished all of those certifications. Wasting time trying to calm down is only going to hurt you more when all you really need to do is hunker down for an entire afternoon and knock them out.
Yeah, you're going to have exactly zero time to yourself that day between mustering and doing all those classes, and I mean zero, but that's the military. Sometimes you don't get to be relaxed, even when you're only doing classes and learning. Take it from me, I was in the Navy Nuclear Power program.
That said: I know a lot of guys who worked out to relieve stress. They hit the gym or went for a run, supposedly worked wonders. Personally this was a
source of stress for me, so I was screwed either way, but chances are you're one of the normal people who gets positive mental benefits from exercise.