The Reds suffered their biggest defeat of the season at the John Smith's Stadium and sank to the bottom of the table, but Wilson claimed his side were "fantastic" for the first 30 minutes.
"For 30 minutes we were excellent and I thought this was our day to really put our foot down on the gas and we did for 30 minutes," Wilson said.
But first-half goals from Keith Southern and Danny Ward were added to by Adam Hammill, Adam Clayton's penalty and Sean Scannell after the break.
"We should have had two or three goals, maybe four goals, in that period of time," Wilson added.
"We had some great chances, but we didn't find the back of the net with any of them.
"As a group, defensively, that was poor. Second half - we were never in it.
"From where we are, we have to take positives from something and the first 30 minutes was fantastic at times.
"The rest of the game was poor."
Barnsley now prop up the table, but remain only two points from safety.
"The only comfort in one respect is we're not far off, points-wise," Wilson said. "We're still in there fighting."