Anyone else find reading so much more exhausting than listening?

I’m about at N2 listening, and I’ve picked up reading now since I noticed the rate at which I was picking up new words through listening alone has dropped.

I have read occasionally throughout my now almost two years studying Japanese, but I never tried to extensively till now.

Yesterday I read for most of the day. Within an hour of reading I was literally falling asleep. I’ve studied other subjects before and I’ve gotten mentally exhausted. I’ve never, ever gotten sleepy when studying. Idk if it’s just that I’m getting older or something, but that has never happened to me. I’ve lost focus, I’ve felt tired. But never drowsy like I feel when reading Japanese. I thought it was a fluke, so I took a nap and started again. After another hour, I had to take another nap. Then today I started reading, and within 40 minutes my eyes were drooping. Another 40 minute nap.

I was not expecting this to be so demanding. Part of me feels good in that I take this as a sign my brain is working overtime, but I’m shocked. Did you also experience this when starting to delve into reading? Any insight is appreciated!