Goals from Daniel Powell and Ryan Lowe - either side of Franck Moussa's equaliser - had put the Dons in charge at half-time before Stephen Elliott's double condemned the hosts to a third defeat in four games.
Robinson said: "I don't think we deserved to get beaten. You'll always get an honest assessment from me and the Walsall performance was no where near where we're at.
"We didn't deserve to lose that, but it was just five minutes of madness. Their first goal was an own goal - he's headed it on to Shaun (Williams) and it's gone in the goal so it's just unlucky.
"But it was just because we didn't switch on for that five minutes - we don't generally concede many goals in that period because we normally come out all guns blazing.
"It was difficult that second half for me because I'm looking behind me, I'm looking on the pitch and I'm thinking what can I do?
"They say they've got no money, but when you look and (John) Fleck coming in and Elliott coming in, who has played in the Premier League, they've got tremendous strength in depth."
Powell put the Dons ahead after 15 minutes when he cut in from the right and drilled a fine left-footed shot inside the far post.
Moussa produced a superb solo goal to equalise for Coventry before Lowe restored the Dons' lead seven minutes before the break with a fine angled shot.
But City striker Elliott scored twice in three minutes shortly after half-time to turn the match on its head, first when he nodded in Gary McSheffrey's cross from close range and then when he fired low past David Martin.