I find that this really fucks with my head. If I think about life, our existence on earth, the size of the universe and so on, it literally messes with my mind & I end up thinking I am a pointless speck in time and space on earth for just 80 odd years in a universe that is billions of years old.
So, I try and think instead, that I only exist in the moment and what I do with each moment (as best I can) is what counts. That doesn't mean I don't plan for the future and I just wander around airy fairy gawping at dust motes and the clouds going by, but it does help me ground myself and try and be present and not overthink the pointlessness of myself!