Possibly a form of dissociation where the line with realty becomes blurred? Do you feel as if you live very much in your mind, rather than interacting with what's going on around you? Is life for you currently very stressful and overwhelming? That could be a contributory factor, along with the tendency to ruminate and worry.
For instance, you may plan to phone A to tell them X, Y & Z and run through it all in your mind beforehand as you're nervous how the conversation may go, you do then phone them, then afterwards can't remember if you actually did tell them what you intended to, because the call was already a source of stress for you before you made it, making you worry how it would go and rehearse it, and now it's over you instantly find yourself rehashing it mentally and emotionally. Probably not a good example, but it shows how easily imagination and reality can overlap and get confused.
Also, do you experience lucid dreaming? To be honest, what you describe doesn't sound like that, but it may be worth reading up on if you're not familiar with term. When I used to have lucid dreams, I would come to the realisation that I was indeed dreaming and, once awake, knew clearly that it had been a dream. But perhaps for some people the dividing line is less clear.
Lastly, I know it tends to get trotted out as a cause of everything, but are you going through the menopause or perhaps approaching it? The "brain fog" and sheer exhaustion menopause can bring for some women, can make you feel as if you don't know whether you're coming or going.
Whatever is causing this for you, I hope it resolves soon.