How do you deal with an existential crisis?

I think it's a fair question to ask. We're all different people and even though we may be going through similar experiences, we're going to deal with them differently depending on our past, beliefs, upbringing and hundreds of other factors that had and impact on who we are.
The reason im asking this question ow is that lately i have been feeling like i dont really belong, like there's something more to life, something i have not yet discovered or experienced and that perhaps im missing out. You know, how when you're a child and you just cannot wait to be a grown up, to do all the things you see them do and just join what seems like a fun party? Well, I always thought that by now I will have it all figured out, life will be exactly how I always imagined it to be - nice flat in the city, job that I enjoy, good friends around.. and so even though I technically have all those things, it seems like something is missing, or out of place. It took me a moment to try to figure out what it is and only a short while ago, I realized that the things that seems to be misplaced is me. As simple, or actually as complicated as that. I'm not happy. Or i dont think i am, but then again, when you have to question it, I think the answer is pretty clear here. Even though I have achieved quite a few things that I hoped for, it's still not good enough. I guess as you're growing up and actually become an adult you've wanted to be for so long, you dont realized that you lose so much during the chase for something that is nothing more but an illusion of having everything under control. Because, when you think about it, in life, we're never actually fully in control. Things always happen, whether we want them to or not, and even when you're at your lowest point, sitting in the darkness of your own bedroom, with a warm blanket on top, life is still going on, everything is still moving - world is not going to stop just because you're feeling low. People die, people leave, you get fired, look for a new job, go broke, get pregnant at the wrong time or with the wrong person, you get ill.. so many things that are, at the end of the day, out of our control. Of course, good things happen as well - you meet new friends, partners, you get that job you've always wanted, see the band you absolutely love, travel the world.. Though, and well, it may just be me, sometimes, when it comes to all those bad things vs good things happening, it seems to me like it's so easy to forget the good, when bad happens. Anyone else gets that feeling? Like now, for example. I moved to the city I always wanted to live in, have amazing flatmates, good friends, got the job I always wanted and I think I'm actually good at, but there's still something that seems to be off. So all those good things that I have worked hard for, are something I now question - do I really need them, is it something I actually want, should I just pack up my bags and move somewhere else, start fresh and perhaps get a free reset of my life?
It's quite ironic, when you think about it, that growing up it seems like all the adults around you know exactly what they're doing - they seem so contained, like they have their all lives together and that's why you admire them and you can't wait to grow up just so that you can play with them. And then you finally do join the party and realize that none of this was real. Not to say, there aren't people that know exactly what they're doing, but let's face it, most of us are struggling? We're pretending to know where in life we are, following the dreams we think we have up until the next one comes up.
Funny how there are so many people, trying to go through day to day life, creating a perfect illusion of bliss and only when they go home (though sometimes not even then) their mask comes off. Take me, for exampled - and I know for a fact that I'm not the only person in this situation; I work in a profession where I'm supposed to be helping people trying to turn their life around - I'm pretty bloody good at it. I have all the answers in the world, I'll sit and listen and talk you through it and then help you look for the best solution. My solutions to my own problems? Ignore them. Bury them under the surface and smile, pretending everything is fine. Smoke a pack of cigarettes a day, pretending it helps with stress. Drink a bit too much on the night out to numb the pain. Get into questionable, short-term relationships with people just so that I do not forget what it's like to have someone next to me, but at the same time keep it shallow enough that nobody's trying to get too close to me and Lucifer forbid get into my head to see all the demons hiding inside there. Sounds like something you can relate to? Funny, how in the world where we talk so much about mental health, we so often actually neglect it and decide to ignore the warning signs. I'm not sure whether it's pride or fear, or perhaps a lethal mixture of both. I just know it's always there at the back of my head.
Anyway.. I started to digress a bit too much now...