YANBU.
I know what you mean. I am pretty much in the same boat. I have only just realised this week that the reason why I used to drink so much in the evening was because I was, fundamentally, bored and unfulfilled, and the drink helped me to ignore this truth. My life consisted of work and not much else, and finances were tight.
I am starting to get some clarity about it though. Somewhere along the line, I stopped being "me" and somehow started living life in a very conformist and parochial way. I was okay doing this, I wasn't depressed, but I was just existing rather than living.
I don't have any clear answers but I do have a few ideas as to how this sort of thing comes about. In our culture, from the moment we are born, each year brings a new experience and a sense of progression. There is always something different round the corner. Learning to speak and walk, going to playgroup for the first time, then starting school where every year means going up a class with a new room and teacher, then going to secondary school where, every twelve months, things change -- for some people that do degrees, this structured academic change, newness and "progression" lasts until they are in their early 20s.
Then there is the first job, the first serious boyfriend, the first flat or house-share, the first child etc ... but you can get to the point in your 30s when that sort of natural progression and change stops happening. Nothing new automatically appears on the horizon. Everything is as it is. Life can come to feel almost static.
I reckon this is where these types of feelings appear. After all, we have been trained throughout our youth to expect newness or change every twelve months, and when it stops happening, well, I think it can really throw us off.
You mention "trudging" and I think that is very telling because it suggests you are stuck and it could be that you feel stuck because nothing is changing in your life, nothing is new anymore. Everything is the same, day after day, month after month, and it feels mundane on a very basic level. Maybe you felt exhilarated in your youth because you were experiencing things for the first time?
Maybe you need to experience something for the first time again to crack these feelings?