“And you did get into the
coffin?”

[X] “I had no choice. I begged Lestat to let me stay in the closet, but he laughed, astonished. `Don’t you know what you are?’ he asked. `But is it magical? Must it have this shape?’ I pleaded. Only to hear him laugh again. I couldn’t bear the idea; but as we argued, I realized I had no real fear. It was a strange realization. All my life I’d feared closed places. Born and bred in French houses with lofty ceilings and floorlength windows, I had a dread of being enclosed. I felt uncomfortable even in the confessional in church. It was a normal enough fear. And now I realized as I protested to Lestat, I did not actually feel this anymore. I was simply remembering it. Hanging on to it from habit, from a deficiency of ability to recognize my present and exhilarating freedom.

– IWTV

It’s up to each reader to interpret that quote as his having just a dislike for small spaces or legit claustrophobia, I interpret it as legit claustrophobia.