Ivar began to wake up slowly. Before he could even open his eyes, he felt a strong headache that nearly made him pass out again. Say that his mind was going to explode was little to describe the pain he felt at that time.
Without getting completely conscious he could already guess that it was because his mask was thoroughly broken. It was, after all, one of the consequences of having the mask shattered.
When someone at District 42 took off their masks for too long or it somehow broke, and that alone was a difficult feat, the person in question would feel like his brain was being squeezed and his consciousness would get somewhat numb. It was a strange, uncomfortable, and painful feeling.
This was one of the reasons why people couldn't just take off their masks or break them. Besides the restrictions of the masks, this punishment was an issue as well. Even if reduced to pieces, the masks could still cause this effect on one's mind.