No. Bad author! This may just be smut, but NO ONE can spend 18 years in a small isolated dark cell with no contact, no socialization, and not end up royally batshit fucking crazy. He probably would have ignored lakshal and immediately proceeded to torment the villagers, then butcher a few of the more disagreeable ones, while possibly eating some of them, then wearing their wet skin while singing and dancing around a bonfire made of clothing items. It is also entirely possible he would have chosen to just stay in his cell, comfortable with what's familiar.
Sensory deprivation lets you see your imagination, and that might be awesome in the beginning, but of all your thoughts and ideas and emotions, the most durable of notions, the strongest of your feelings is FEAR.
And that is exactly what he would be tormented by day in and day out, year after year after year after year. There are prisoners who have actually been subjected to torture like this. They become something less than human. They can barely think, let alone function. They babble incoherently, or shriek at the littlest of things. The boundary between the waking world and their nightmares no longer exists, and the hallucinations become real.
It's a fate worse than death.
... should I also mention that he also likely smells so bad that others would want to vomit if they got close to him, but he probably doesn't smell anything?