Then you start wondering if you, or anybody, have forgotten anything so important that it would shatter your world.
And would you ever know? Is there any way to ever know?
What if the past changes as much as the future?
What if that's the Mandela effect?
It is about an intelligent person who is confined to live with only 7 second memory. He keeps a diary recording his entries. As he reads past entries, he realises the predicament he is in and considers that his case would be interesting to doctors. Then forgets all about that. Rediscovering the whole thing again in the next 7 seconds for himself anew.
44:20 @ https://youtu.be/k_P7Y0-wgos
This instance of a poster's existential pondering is not mental illness. It's a valid question. The answer was yes. See repression, then research other cognitive distortions. It's part of building up a healthy meta-cognition.