Although I know you've consulted your previous question and the answer provided there, I'm going to refer to that answer to (try) and answer this one.
In the Season 3 episode Fly, Walter states:
"This fly is a major problem for us: It will ruin our batch, and we
need to destroy it and every trace of it so we can cook. Failing that,
we're dead. There's no more room for error, not with these people."
Now, whilst out of universe it's well known that a key driving reason for the episode was a lack of budget (as Gilligan, the show's creator has stated in interviews), in universe Walt's comments show how it symbolises the perception of losing control.
Gilligan expands on Walt's comments in an interview with Vice, stating:
The reason in our minds that he was suffering with his own form of
post-traumatic stress was that he had recently learned of his
inadvertent responsibility in the shooting and wounding of his
brother-in-law, Hank. He found out about Tuco’s cousins who were out
to get him and he found out that Hank got in the way of their shooting
and found out that indeed Gus Fring gave Walt’s brother-in-law to the
cousins instead of Walt himself. In that moment of powerlessness, in
that moment of shared responsibility and that moment of realizing just
how culpable he was, and just how he would have to suck it up and grin
and bear it to this very dangerous man who he thought was a very
business-like, very rational man. Then he finds out this guy is
rational to the point that he’s almost sociopathic. “My brother-in-law
is now in danger and everybody is a pawn to this guy and I’m trapped
here and I have to grin and bear it.” It’s the old Godfather line,
“Keep your friends close and your enemies closer.” So we had that
episode in which he goes to Gus and says, “I know you essentially
ordered a hit on my brother-in-law, and I know why you did it, and I
want you to understand that I’m fine with it and I would have done the
same thing." Of course he wasn’t fine with it, because then he got
into his car and almost drove into an oncoming semi. That craziness
you’re speaking of really all stems from that moment. It was a
craziness that derives from “I’m really trapped here. I don’t like
this feeling of being trapped. How the hell do I get out of this? How
the hell do I live with this guilt?”
So clearly the fly in the episode The Fly symbolises a terrifying realisation on Walt's part that he is not in control and a fear of where this is leading him.
Now, relating that your question about the Season 5 episode Gliding It Over All, I would suggest it is to again symbolise a lack of control.
In the finale of the previous episode, Say My Name, Walter loses control and kills Mike Ehrmantraut. In the opening scene of Gliding It Over All, he is fully appreciating how significant what he has done is and realising that once again he has placed himself in dangerous territory.
This time though, unlike in The Fly, his lapse is very temporary. As soon as Todd enters, he begins to compose himself and is able to start conducting operations.
I believe this indicates that he still senses the loss of control (and even regret) over what he has done, but that he has come a long way from the person he was in The Fly and he is able to process these feelings and respond to them (in a ruthless manner).