One of mine was within the first few weeks of being a medic. I was pulling a reserve shift with a neighboring FD, and dispatched to a "sick person, difficulty breathing," Pt being around 16 yrs old, female. Enroute, my experienced and fulltime EMT-B partner (FT with this department), we got turned around and zigged when we should have zagged. By this point, dispatch came back and told us they were dispatching a second unit and giving CPR instructions.
U/A, found pt supine and unc./unresp. Nice sinus rhythm, maybe SLIGHTLY tachy (it's been awhile), and basically everything "within-normal-limits." Then...Pt wakes up, starts to talk, and goes out again! She does this repeatedly several more times, and I finally said we need a helicopter (C-3 transport to nearest hospital about 25 min away). I called for the helicopter within 5 minutes of getting o/s.
So...QBing this with the more seasoned medic (and one I HIGHLY respect), we figured out she was hyperventilating, and it was the lack of CO2 that was causing her to black out.
My justification for the helicopter was that she was 16(ish) and I couldn't figure out what was going on...so err on the side of the patient for the quick transport time.
I'd have hated to be in her house when she got the bill and the cycle repeated itself!
Now...I took what I learned from this and have not made this "mistake" again!