It can mean many different things. A lot depends on your age, stress, food intake, and exercise. There are metabolic changes that occur several times in our lifetimes. Some gain weight and others lose. The main fear of sudden rapid weight loss is cancer. So, with that in mind, you need to get examined carefully by someone who is knowledgeable in the area. This likely will require a referral to an oncologist or internal medicine specialist. Many doctors no longer know how to do an exam any longer. Very few require disrobing and are 100% reliant on laboratory tests for their diagnosis. They were trained in it in their internships but modern medicine doesn't stress this any longer. I remember the last time I was at an American clinic in the US they did my blood pressure without having me roll up my sleeves so total theater. I was chuckling as this is how American medicine has evolved into elaborate theater instead of medicine. They gave me a BS number for my BP and I knew right then and there what was what.
One of my early mentors who was very cynical pushed that 99% of illnesses cure themselves so it isn't very important to actually perform medicine but rather to convince patients you are doing a wonderful job for them. So, in his view, it is more important to not do harm and to just let the patients feel good, prescribe harmless medications, and let them go on their way. If it is serious they will come back later. I do not adhere to that concept but it is better than treating unnecessarily which also happens a lot especially when the practice of medicine is a business and not an entitlement or social program. This is the benefit of single-payer (national health plans) that take the profit out of the equation.
It is actually interesting as I am old school and was trained that way in the 70's. The old look, feel, touch, and smell still works but I haven't seen any doctors in the US do that for a very long time. But, moving here to Hungary I was delighted to see them require full disrobing, a full-on physical exam with palpations, and they require a urine sample that they look at and smell. They perform a quick blood pressure and while doing that watch you carefully, examine eye pupils, breathing, etc. They do all of this themselves and are not reliant on semi-professionals to do it for them. It is how I do exams myself and how it should always be done but rarely in the US as they simply are not allowed any time for it. Here there are no limitations to a patient's exam time. Really, it is wonderful to see medicine practiced as it should be.
The bottom line is to go get examined. Early detection is the key to beating cancer. Don't let them BS you out of doing it.