I agree about how surrendering the lead impacts confidence, really hit us in the Spurs game for example. But think the fitness part was only true early on in the season, there were several games just after that we were the better team after the 75 minute mark - Man Utd and Liverpool for example. And recently despite being down to 10 men for an hour imo our fitness was great against West Ham. In both Man City games I thought we finished the stronger team as we did versus Crystal Palace last weekend.But it's all part of the big picture though, we were under cooked for the first few games...confidence drops..players try harder and push themselves more even though their fitness isn't upto scratch and they put themselves in danger of injuries... like Lukaku at the begining of the season, like Stones and Coleman coming back to soon before Christmas and like Mirallas and McCarthy now, all important players.
For the last 8-10 years we've always had our squads fitness to bail us out in the dying minutes of games but since the start of this season we've looked knackered after 75 minutes. I hope this trip to the training camp sharpened them up because possession based football's principles is based on tiring the opposition out, but all it seems to be doing this season is running us into the ground.
Players coming back too soon in their recovery is a different issue and one that has definitely hit us hard but haven't noticed a persistant problem with late game fitness, especially not recently.