I had a TTT and by it the tachy seen on my holter was diag as Inappropriate Sinus Tachycardia, I was diagnosed with neurocardiogenic syncope, too. I am now treated for both and feel much better.
It can show the different mechanisms of syncope or near syncope, lightheadedness. It can help diag POTS, too. There may be other things, but I don't know.
You may be able to get a little more info at the NDRF site.