Sorry for not seeing this earlier, I have been away with the military alot over the last month and a half.
First off, the steroids could be responsible for the leukocytosis (elevated WBC) and this could be a relatively quick response (as it is believed that the steroids affect the adherence of the WBC to the blood vessel walls, making it look like they have suddenly increased). However, I would expect this to subside quickly and thus should not be present in further blood work.
I would have a hard time excluding cardiac syndromes in the face of your story, without "casting eyes upon you" myself. Mind you, it is completely in keeping with a viral syndrome (run of the mill virus) that resulted in a labrynthitis. I would expect the shortness of breath on exertion and palpitations to be in support of this (as well as a million more dangerous things).
The yard-stick I would use to determine whether to seek further care would be that a) it isn't resolved already, considering this was over a week ago when you wrote this or b) if it continued to get worse (decreasing levels of activity resulting in similar symptoms, or symptoms getting worse at a standard activity level.
Beyond that, providing they did a reasonably-full cardiac work up, considered clots in the lungs, clots in the brain, narrowings of the carotid arteries, pneumonia and aortic artery conditions (and it seems like they probably did, considering these conditions doesn't necessarilly mean throwing every study imaginable at them....maybe just being reasonably certain you don't fit the MO of such things), I would say they would likely catch all the dangerous stuff.
I hope this helps, but considering this was a week ago you posted, I imagine you aren't in need of my help anymore.
