After a run of three successive wins, Barnsley went behind in the 18th minute when Yakou Meite struck from close range.
Top scorer Cauley Woodrow could have levelled for the visitors but squandered several first-half chances.
Reading increased their lead on the hour when George Puscas raced through to fire home.
Barnsley now lie five points from safety in the Championship and Struber said: "I'm disappointed. The first half was okay, we made good chances but we didn't score.
"In the first 20 minutes we had control on the ball and good positioning.
"But in the whole game, we did not have the right energy for sprints or for the right moves.
"In the end, we did not have the big conviction that we needed so that we can win away against Reading.
"Some players were only at 90 per cent – or lower – and that was not enough so that you can win this match.
"The last games for us were very hard and I think that we lost energy from them.
"In a normal situation, I think that we can bring more intensity.
"But we had no intensity, no high-speed running. This was my feeling.
"It was not difficult for our opponent and this was the problem for us. Without this energy, it was just not enough.
"We had created very good performances in the last three games, we had a high aggression.
"But today the battery was low. We were not ready for a big fight here. It was too easy for our opponent."
After a 3-0 home defeat to Wigan on Wednesday, Reading secured only their second victory in 11 league outings.
Boss Mark Bowen said: "It was important after what happened on Wednesday. I think we've put that to bed now.
"Since I've been here, I think that Wigan game was a one-off.
"If I'd been a supporter for that, I'd have vented my anger just the same as the fans. It was unacceptable.
"Today, for me, was more about getting the result.
"Just to calm the dressing-room, if you like. To instil a bit of stability and confidence in there.
"We may have won the game 2-0 but we weren't quite flowing as we can. Passes were going astray and we were a little sloppy at times.
"But every team in the league can go through a period of games when things aren't going their way, when one or two players have lost confidence.
"When you hit those periods, you've got to make sure that you do other things right.
"You have to make sure that you're professional and your decision-making is right. Then you get results.
"Going into this game, I was saying a little prayer that something would happen for us.
"And the first goal was like that. It was scrappy but it goes in and gave everyone a bit of calmness and confidence from then on.
"In the second half, it was a question of going out there and doing the right things and not being sloppy.
"George [Puscas] got the second and that's just what he is – a goalscorer."