What is the smartest way to fake a sickness?

Ok I’m 19 years old and my family is coming over for christmas and I have some personal reasons as to why I need to play sick which really do not matter. My question is what sickness is the best sickness to fake to keep me home for about a week without having my family feel bad for me. Because i want to pretend I’m sick enough to be able to not have to go anywhere with my family when they go out and about but at the same time I don’t want them feeling sorry for me or worrying about me, I wouldn’t want to do that to them. It would be a type of sickness that would keep me in bed for the most part but not too sever like the flu or something. that would be too much.

And also, I would appreciate it if you didn’t just give me the best sickness to fake but if you gave me your input on the smartest way to do it, as in how to go about doing it

Now a good one I thought of was something like faking a type of stomach ache that I “just” tend to get every day? Because that’s not something that can exactly be measured with the little thermometer you know? or maybe even a headache, but that’s not strong enough to last me a week! So they wouldn’t be able to tell if I’m lying or not.

P.S. please don’t tell me what I’m doing is wrong or whatever, I’m not looking for advice in that area. I just need to be able to have a good enough reason to stay home when they leave the house to go out and about, and that would KEEP me home for a week at the least, and playing sick is the only valid enough reason I can think of…please help thank you!