I 100% know what you mean. I was a hikki for longer than I've been out of it, but all the years I spent as a hikki feel like probably 1/30th the time that I've been out of it. It was a really jarring transition because, when I was a hikki, time felt normal if not kind of blurry and mundane. But after maybe a month of having a job I noticed that my memory of all those years got extremely blurry and what felt like a few years suddenly felt like maybe a year at the most, and the longer time went on the shorter my time as a hikki seemed. My guess is that the life of a NEET/hikki has so little mental and physical stimulation, your memory only has so much to work with to form memories, which would also explain why time seemed so blurry and monotonous too.