** Spirit Airlines' FLYY.A shares fall nearly 44% to $1.97
** Co warns of going-concern doubts, just months after emerging from Chapter 11 bankruptcy
** Elevated domestic capacity and weak demand for leisure travel in the second quarter has resulted in a tough pricing environment for the airline
** Co expects these pressures to persist through the rest of the year, adding to operational uncertainty
** Including session moves, shares down about 77% YTD