A little about me:
I'm on the autism spectrum; I have tiredness issues and other related problems. I'm currently working full time and this plus my tiredness makes it really difficult for me to eat in a healthy way. Also, still due to my tiredness, I'm not doing any sport and usually don't do much during the weekend.
My family knows all of that and is worried about me.
Some time ago, I was at my grandparents' house for the weekend and on two different occasions, my grandmother told me:
I'm worried about you.
To which I only responded with "okay".
I'm bothered by the fact that my "okay" was too cold and sounded like I didn't care. I do care, a lot, but I didn't know how to answer. I'm worried about me too, but I didn't want to make her even more worried. At the same time, I didn't want to tell her "you don't need to worry about me, I'm doing fine" because that would have been a lie.
How could I have answered her in a way that didn't sound cold but without minimizing things nor making her even more worried?
If possible, I would like to express to her that I'm glad she cares about me. However, I'm afraid that just saying that would be a little weird and make her even more worried about me.
About the setting:
I don't really remember what was the setting when she first said that to me but I believe we were alone.
When she said that to me the second time, we were eating with my family (grandparents, parents and sisters).
If I remember correctly, I believe she said that after we talk about the fact that I wasn't eating really healthy in my home (I always eat the three same pre-cooked stuff).
Notes and clarifications
I would love for someone to care for me, e.g. cook something healthy for me or take me out to sports in a way that I like. Unfortunately, my family lives far away and this isn't possible. Also, my grandmother doesn't cook anymore (her food is delivered at her home every day).
When it was discovered that I was on the autism spectrum, my grandmother took it very well and didn't doubt it. She knows me very well, even if she doesn't necessarily know that some of the particularities that I have are linked to my autism.