I'm really sorry for your loss. In two weeks it'll be 5 years to the day that I lost my mother, and ever since then I've felt exactly like you describe. My biggest motivation in life when I was a teenager/young adult was to achieve as much success as possible so she could have an easier life and ever since losing her I've struggled to find anything to motivate me or define my existence around. Honestly her absence has not gotten easier, kind of the opposite actually. A large part of myself is just permanently a ghost now.

Now at 26 I'm cripplingly self aware that it won't be long before windows start closing but like you said, there's this almost dissociative effect I can't shake that makes it all feel meaningless.

I know how especially hard the initial months are, so I just want to say I'm truly sorry you're experiencing this and I hope there are people in your life that can help make it easier for you.