Starting from the Cadet Corps, you experience gaps in your memory. Some sort of 'entity' has made itself home in your mind and as the story progresses, there are certain triggers that have yet to be noticed by you.
First of all, the triggers have something to do with family. Specifically Eren and your close friends. An example is when Eren got kidnapped by the Warriors and you practically made Bertholdt go insane.
Even when Eren got taken away by the Rod Reiss, you made it your job to make sure Eren gets out unharmed, so the entity in your mind jumped in to... 'take the reigns.'
In the Battle of Shiganshina... Well, you don't know what happened. You were on your way to Bianca when suddenly, it was like you disappeared. That's when the loops started to mess with your mind.
But Adele and Ilse will help you get back to the best of their abilities.
They'll get you back home, hopefully.