The dictionary you linked says "the quality or feeling of being grateful or thankful:"
Grateful being: warmly or deeply appreciative of kindness or benefits received; thankful
Thankful being: feeling or expressing gratitude; appreciative.
If you got a benefit of still being alive and you appretiate that benefit, you can be grateful. It's not necessary to identify an agent who's responsible for the benefit. The imporatant thing is that there a benefit and you appretiate the benefit.
Well, I used to think that I do not believe in anything supernatural that affects what happens to me, but I'm wondering if maybe I actually do alieve in it. For example, a few days ago I had a close call in traffic, and when a collision I fully expected to happen just a second prior did not transpire, I mentally thanked... whom? I definitely had a clear feeling of gratitude for escaping, and I don't normally mean it literally when I say "Thank God!". So, who or what did I feel thankful to? I've never been religious, and I got rid of most of my superstitions over the years, but apparently there is still something there, and I do not know how to react to this knowledge.
What would be the proper reaction after a close call? Shrug and say "got lucky this time, should be more cautious next time"? What about when waiting for a diagnosis, what does sort-of-praying "please, please, let everything be OK" say about one's true beliefs? I know that I am much better at not blaming the world when something bad happens to me by chance than at not thanking the world when something good happens. Should it not be symmetric? Which part of a normally non-religious person wakes up and asserts itself in a crisis situation out of their control? Should it be embraced, suppressed, worked on?