K.P.
I'd probably wait one missed cycle to see if I just "skipped" a cycle and resume in 8 weeks, but after that I would want to know what was going on. My SIL died of colon cancer when she was 35, and her "missed period" was one of the early signs that something was wrong, but she ignored it. (I think the cancer started in her colon but moved into her uterus, which is why her periods stopped; I don't think it was just the cancer in her colon that did it.) She also started losing weight effortlessly, but was glad for that, having always struggled with her weight (I guess she thought her metabolism was kicking into high gear for some reason?)
Most likely, it's not cancer or anything majorly wrong like that, but it's not normal, so I would be looking into it, in case it's a signal of some underlying health issue that *is* a problem.