Something lingering on my mind.

Two days ago, I was having a conversation with my father, who rarely comes home recently because of his heavy workload.
He and I were standing near the refrigerator in the kitchen, and he was telling me about how he has to go back to work at Batam again the next day(which was yesterday).

Me: "What, again? But I rarely see you anymore!"
Father: "Yes I know dear, but it can't be helped."
Me: (sigh) "When are you coming back?"
Father: "This Friday, to accompany mama to the hospital for a checkup."
Me: (eyes widened)"Oh, a checkup? What for?"
Father: (takes my arm gently and puts it against his side. There was a pause as he looks at the fridge, and his grip on my arm became more firm. I looked away and waited quietly for an answer.)
Father: "Just a normal medical checkup, dear." (avoids eye contact)
Me: "...Okay." (starting to grow suspicious)

Then we changed the topic to how my older brother was now learning to drive a car.
Obviously I wasn't convinced with the previous answer my father gave me, so I asked my mother who entered the kitchen.

Me: "So ma, you have a checkup this friday?"
Mother: "Ya. Your friend is coming over this friday right? So you guys will settle your own lunch and all."
Me: "Yes ma. So what kind of medical checkup is it?"
Mother: "Just a normal medical checkup la."
Me: "...Okay." :/

I decided not to press the issue further on, but I had a strong feeling that they were hiding something from me. At the same time, I really hoped that I was just overthinking things, and I was wrong. I decided to try one last time the next day, when I saw my mother trying to bend her finger in the kitchen. She told me how she had difficulty bending her fingers, and says it's probably a matter of time before she starts experiencing pain in them.

Me: "Oh...that's bad. So is that the reason why you need to go for that checkup on Friday?"
Mother: "No la. That checkup is for other things."
Me: "...O...kay...."

Fine. As much as my curiousity is killing me to find out, I stopped pressing it further. Ever since that conversation though, it has always been in my mind, with this big question "floating around" asking: "Why does my mother need to go for a medical checkup and what is that checkup for?"
Please do not let it be something serious. That is all.