I am not so sure, but in the latest chapter, the MC's old manager was there with the ML in a club or some. In there we can see him giving a "happy" drug to ML, and he explained that ppl who take it wouldn't be happy without it or wouldn't be able to feel emotions without it, or like when they see light, they will, yk feel irritated and stuff; these are all the things the MC is currently feeling and experiencing. In this chapter, we also see a glimpse of the previous chapter, which hints to us that he is currently unable to "feel" emotions, and in the first 3 to 4 chapters, they show us that he cannot stand the light. So if we think about it, it can mean that the MC took the drug or someone gave it to him without him knowing. (Maybe without knowing.) But I am not so sure; this is my theory. ( ̄へ ̄)

The way I connected the dots so quickly, I can't. Honestly, I thought that it wouldn't involve stuff like drugs, so it is quite surprising for me. Σ(  ̄□ ̄||)