Migraines are better, but SIL doesn't want me to babysit

Long story short, I was "restructured" out of my job because of migraines. And I'm at retirement age so just threw in the towel. I have been using magnesium patches, a patch called Vivarin, and I have time to take better care of myself, not having work stress has helped 100 percent. I get one here or there but usually weather or bright light or sun related (I'm photophobic, but found purple glasses really help). Motion sickness is still bad, but not as much. Daughter and SIL are planning to have a family, I have been lined up as the full time babysiter since they even talked about having kids years ago. Now all the sudden, because I didn't visit my SILs cat yesterday...my daughter said they are really worried about my reliability as a sitter. Even my husband said that was BS as even if I did have a dibilitating migraine (or the flu, etc. for that matter), he can step in. Hubby and I worked opposite shifts when our kids were little. He is great with babies, tots, you name it. I married him because he loved kids, so he's my back-up. The way my daughter talked to me about it was like I was mentally challenged anymore so they were worried about me and I'd have to show up every day, and they are worried I won't (get this) because I don't visit their cat everyday. The damn cat is so neurotic it won't even let me hold it. (Poor thing is a rescue). So basically if I'm there, I end up cleaning or bringing a book. And, I did plan to spend a year just "relaxing" as I know babysitting will be back to a full time job. So visiting a cat isn't really on the top of my to do list right now. However, it was my dream to raise my grandchildren (sorry if that seems pitiful to some people, but the chance to influence another human, see them grow into fine adults, its my passion). We have four grown adult children and are a close family. We are not perfect, but I know the priviledge of caring for a baby, toddler and on up, and I love being there for them as my parents were never there for me, so I know how it feels. I probably overcompensate in that area. We agreed it would work, but with their hesitancy. And now I feel "fired" all over again (sort of PTSD prone I am), and it's just not the same. Makes me nervous, like they have no confidence in me. And it's what I planned my retirement around...and was so looking forward to it, it took the wind out of the sails that's for sure. AITA for feeling this way?