Wales coach Warren Gatland said he considered making drastic changes only 25 minutes into the 25-21 defeat by England at Twickenhham.
Wales fought back from 16-0 down at half-time with late tries from George North and Taulupe Faletau but the scoreline flattered the visitors, who were totally dominated by England in the first half.
Despite all the talk of a Championship decider, Wales were surprisingly lacking in intensity and hunger before the interval and Gatland labelled their display as "totally unacceptable".
"I just can't explain why we were so flat for those first 40-odd minutes," said Gatland.
"I said to the boys at half-time they needed to show some energy and enthusiasm, and to come up with some answers themselves.
"After 25 minutes, I sent a message asking if we needed to make some changes and get some fresh legs out there. it was really unlike us - a really poor first 40 minutes
"The way we performed in that first 40 minutes was totally unacceptable at this level. The players have to be honest with themselves, because we prepared well and it's hard to understand why we looked so tired and lethargic.
"At this level, when there is so much at stake, you need to have the right emotional state as you take the field.
"We'll be thorough in questioning our preparations. The players will hopefully be honest about their own performance, particularly in that first half.
"That is so unlike us. But I'm proud the boys didn't give up and they kept their heads. In the second half we got some impetus and finished strongly and we wonder what could have been.
"England competed hard. We outscored them 3-1 in terms of tries but it was Farrell's kicks that were the difference. The best team won and I take my hat off to them."
Gatland also revealed his captain Sam Warburton, who was carried off on a stretcher in the second half after suffering a head injury, was sitting up again in the changing room afterwards but will go through the sport's concussion protocol in the coming week.