I don't know about you but I often have the feeling (especially at the moment having just moved to a new country, town etc) that I am only one step away from disaster, and that it wouldn't take much for it all to come falling down on my head. But that is usually when I am obsessing too much about myself and how my life is developing. It's not really on an existential level though.
Listening to the news about the fires in California this morning on BBC World it really struck me that we are all only ever clinging to the surface of this world. Our grip is never more than tentative. It doens't take much to wipe out a town, a state and your whole life. It sounds trite but it does remind you that we are all human and that in the face of disasters that is all that really counts.
I am sure some philosopher somewhere will have talked about the importance of realising that. I know that it's a large part of the Bible: humility because none of anything that we have is owed to us. But a lot of life at the moment seems to focus on avoiding the thought.