Loss of focus and conditioning most likely. Very much sounds like end of season burnout. Good rotation in Jan/Feb can prevent this. keep your best players fresh for the big finish
I play the game as realistically as you can and never have been a download a super tactic and plug and play away to success.
I have tried to come up with a good footballing reason for this to happen. I want to know why it has happened so i can prevent it from again in a future save or again in this one.
I did rotate my squad as i had a 30 point lead over 3rd in january and i like to anyway to keep all my players happy and to keep them improving in training as i usually prefer younger players to help develop them. I also had a team meeting after the first two losses of the slump and all players reacted well but we still carried on getting beat. The overall player personalitly for my squad is ambitious i thought i would mention. I can take having a loss and sometimes i prefer to have one as it can help to address any weakness but i have never experienced this in 8 years of playing fm and i do realize 13 is a completely different animal to the other versions but is this the realism everyone was after?