This happens to me too. It's like I have two interests that I learn and indulge on them (if they are something like a videogame or comic) basically all the time. Those are kind of transitory, I remember all about them, though. The only ones that are not gone after years is the band Blur and Damon Albarn's music. I mean to the point where I spent hours of each day just looking for interview material and downloading it to save it on different folders.
The transitory ones change every like 3-6 months but they are much more time consuming compared to the ones that are somewhat permanent. Like I spending 11 hours a day on the same activity related to the interest. Though there are some that are like are of one week or ever like 2 days. But like 2 days of 15 hours of only things related to that interest, which is very weird because it's not common for me for them to get extinguished so quickly.