Hey, that really sucks. Feeling that hopelessness.
Worse even is if you think that you're feeling like this all alone.
I have had moments like these, and they feel very dark. It feels like you won't be able to get away from it. As if it will always stay like that.
But you really can get past that feeling. There is hope. It's not easy, though.
First, something that sounds bad
You're right, it is all meaningless-- in a sense. Just like a single molecule or a rock, we humans mean nothing to the universe at large. We are so insignificant that it can be the most depressing thing you can think of.
That's why it is so essential to make the world smaller to yourself. Only focus on what you can control.
It is not much different than when a child learns to walk and explore the world. Suddenly there is so much more they can see, but also so much more they cannot yet have control over.
Making the world smaller gives you back control (see this short clip from 'Man of Steel' that I think is relevant). And when you feel comfortable, you can venture out again and make the world a little bigger.
But a smaller world is only a part of the solution.
That depressing, meaningless feeling can remain (partially) if you don't also do something else (next to making the world smaller). It is something you may find hard to do when feeling depressed or in an existential crisis.
You see, if the universe, humanity, --everything-- has no meaning, then it's your choice to give it meaning.
Even keeping open the door for someone behind you is meaningful to someone else. In turn, this gives purpose to your own life--in that moment-- even though it feels as if it is not enough at first.
These tiny acts compound, giving you a sense of purpose again.
You do matter, and it does matter what you do in life; it does matter that you are here-- in this universe, on this planet, in this country, in this city, in this street, in your house-- You are giving meaning to others, and through that, to yourself.
I know I know, you may say, "Some others provide even more for humanity! Just think of Elon Musk's work!" etc., etc.
But opening the door for someone vs. building rockets is not much different if you look at it from the perspective of the whole universe.
What does matter is where the acts are coming from. It all derives from love.
Love for the people in the world, love for humanity, love for a fellow human being that has their hands full, and you know how nice it is when the door is opened for them.
But most importantly: Love for yourself.
When you love yourself, you forgive yourself. You won't be so hard on yourself.
You don't have to save the world. You only have to take ownership of your own life. When you have that, maybe after many years, then venture out a bit and see what you can do for others on a larger scale.
You don't have to carry 'the world.' The world is made up of individuals, all with the responsibility to make themselves fulfilled and happy first.
It is astounding how much meaning and purpose we can create for ourselves in a universe that feels so insignificant.
But it starts with you. Only you can give meaning to your life.
So, take it easy, and you'll be alright.
PS. This was a reply to someone on the web that I thought could use the view of someone that also went through thoughts like that. I'm posting it here also, for people that may struggle with this also.