Thrust into the action as a 20th-minute substitute for the injured Stephen Jones at Lansdowne Road on Sunday, Henson was forced to play the unfamiliar role of fly-half.
After a season wrecked by injury and suspension it was only Henson's fifth game since the Lions tour and he struggled to cope with the intensity of the game.
"When Stephen was on we were playing really well," said Henson. "We were in the lead and if Stephen had stayed on we would probably have won the game.
"I let myself down and I let the players down. They might not say it, but I do take full responsibility. It's a bit harsh, but I am a bit down about it."
Henson's kicking from hand was poor and with Wales under pressure he struggled to pick the right attacking options.
He will not be a keen observer when it comes to analysing where it went wrong.
"I don't really want to watch the video tape - my confidence is low enough already," he said.
"Fly-half is a big role - Stephen does a good job of that and it showed how much we missed him when he went - and I didn't make the right plays or the right calls.
"I was always in two minds. It has been a while since I last played 10. There are loads of excuses - but I didn't perform.
"I made a lot of mistakes and at international level they get punished. It was a harsh learning curve.
"I feel disappointed for myself, my friends, team-mates, my family, my coaches."
Henson required groin surgery last autumn and after only three games back for the Ospreys he was suspended for 51 days for elbowing Leicester's Alex Moreno.
It was a gamble to include him for the Ireland game, but the extensive injury list left Wales caretaker coach Scott Johnson with little option.
Henson will be released to play for the Ospreys against Cardiff on Friday night but admits he is still a long way from being the player who stole the headlines in last year's Grand Slam-winning team.
"I need game-time but it is really high profile all the time and I have to learn quickly," he said.
"It is nearly March and I have only played a handful of games since the beginning of the season.
"I don't deserve to be there (in the Wales squad to face Italy). I have no form, haven't played any games and am nowhere near international level.
"Unless things change on Friday night I don't deserve to be involved again.
"I think I got in on the reputation I built up last year.
"I am some way off that now but I will keep on playing. I will never turn down places in squads and I will keep putting my boots on and getting out there."