I assume you are young based on the way you worded your question, so I will tell you that over the years your interests will come and go. When they go, they rarely disappear completely, and they often come back - sometimes decades later. As others have said on this thread, that's not necessarily a bad thing because it means you are trying different things.
My interests over the years have included playing music, live sound, comics, photography, zoos, and birding. I went 20 years without playing music and just picked it up again recently. I lost interest in comics in college and sold my entire collection, but now I have more than 10,000 of them filling my study. I spent much of 2011 and 2012 birding then got burned out and have not done it since May of 2013. Most likely I will go back to it at some point, but who knows?
But to your original question, the only way I can imagine that someone would lose complete interest overnight is if someone decided holding animals in captivity was wrong and wanted nothing more to do with zoos. Usually interests fade over time and may resurface later.