David Ball scored after 10 minutes for the visitors with a cracking right-foot drive from 25 yards that gave goalkeeper Jake Cole little chance.
Two minutes later the Fleetwood forward beat Cole with a deft, left-foot strike from outside the box that curled into the top corner of the net.
"To go two goals down so early was the problem," said Sheridan. "Two goals so quick, at that time, we just didn't pick up after the two goals and full credit to Fleetwood who kept catching us on the break.
"We just totally switched off. It shouldn't be the case it was only 2-0 and there was still plenty of time with 78 minutes to go.
"I am the manager and sometimes it's hard to say things on the reason why. I can look at it and I look at myself sometimes "did I pick the right team?" It was the same team that everyone said played so well at Birmingham in the cup in midweek.
"We have just got to take it on the chin and take the criticism, which I expect because the two league games we have played have just not been good enough.
"I think other than Durrell Berry, who has started the season well, none of them are playing at the level I expect.
"In the league, especially at home, the crowd want us to get off to a good start.
"We are very disappointed and now we have got to pick ourselves up and get ready for probably the toughest game we will have, against Cheltenham away."
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