You actually can get an atma in only a few fates. One of mine in la noscea dropped after only 2 fates. That being said, I've been working on the atma in central thanalan for four days and still havent seen it drop. It's completely random and very frustrating.

I can see why you wouldn't want to be left behind. I'm having that issue myself. Most of my friends either have their animus/novus or are at least working on books. I can't even get all the atmas yet. There is the option of going after the weapons from coil/ramuh/levi instead, but I would like to move past this stupid atma part with RNG and work on books. My myth tomes are just being wasted at this point when i know they could go towards books.

If this is affecting your health, I suggest taking a break. Usually you can feel when a seizure is right about to happen. I suggest doing like I have to do a lot of the time. Farm for an hour or two, then get up and grab a snack/nap/restroom break (whatever gets you away from the screen for a couple of minutes), and then come back and try it again. If it gets frustrating then switch to another task. Run a dungeon/fish/craft and then switch back to the atma. Long sitting sessions aren't good for any players, seizure or not.