Well, nowadays I just try to be aware in the moment and not focus on meaning, the future, etc unless I need too. Success varies.
If I'm too hyper-focused on something (like coding) for too long though sometimes I'll still get a similar feeling. Haven't found anything to do in that case but wait it out.
I also had an experience where the existential depression went away. I thought this comment on the original article described it pretty well:
The solution to existential depression is counter intuitive, which is probably why it isn't well known. Existential depression is caused by wanting to have meaning when a part of us knows that meaning doesn't exist. We grow up in a life where everyone around us jumps from one 'important' and 'meaningful' thing to another, never seeing the pointlessness of it all. We think this is normal so adopt the behavior, but we constantly fight ourselves because part of us sees how pointless it really is. Our base state is where we see how pointless everything is. However, this state does not create existential depression. It's the conflict between the pointless state and the part of us that wants meaning that creates existential depression. We enter suicidal states only when we are unable to find a solution. (i.e. we are unable to find something that has meaning.) The solution, which is now obvious, is to remove all feelings of meaning and importance so that we return to our natural state. If everything is meaningless than everything is unimportant. If everything is unimportant than nothing is more important than anything else. When the feelings of meaning and importance are removed, our existential depression disappears.
Basically it felt like the abstract notions I had been worrying over were indeed meaningless, but that the meaningful world from when I was a little kid was still around, when I could capture the same intense non-verbal awareness.
If I'm too hyper-focused on something (like coding) for too long though sometimes I'll still get a similar feeling. Haven't found anything to do in that case but wait it out.