I think this is definitely part of the process. Being initially somewhat "blinded" by all that material on the board in the middlegame and yet not allowing yourself to be overwhelmed is indeed progress. In such situations, calculate, calculate, calculate. The more you work through it the more comfortable it'll be.
Personally, the very best position for me to win is right before the first move. After that it's usually all downhill. ;-)
I still class myself as a beginner although I've been playing on and off for years but this game takes a lot of time to even get mediocre!
I play a lot against players online and always find that if the board is too full of pieces it's overwhelming and difficult for me to keep track of everything and in this situation I would probably lose.
On the other hand if there are fewer pieces I am much more likely to win as I've done quite a few lessons and read some books on end games and the more I practice the more I am able to quickly see which pieces to move to win the game.
Is this a beginner's difficulty and will I get better over time of being able to cope in mid game?
What do you find is the best position for you to win at chess? Beginning, middle or end?