[He gives a little scoff at the idea that he's doing this for sentimental reasons. Hah, that's a good one.]

The latter.

[Since Lamorak is asking he might as well explain it. It's not like any of this is a secret, after all. His Maker isn't going around broadcasting any of it to the castle, but he certainly isn't trying to keep it hidden. It's important medical research.]

I've got a goddamn brain injury, and who the fuck knows if it's going to get better or worse. Having a record of my symptoms gives my Maker another way to analyze what's going on up here - [He taps his head] - and if there are any changes with different treatments. Writing it down just makes it easier than relying on what he feels through our blood claim, or me remembering everything.