The Magpies are hovering just about the League Two relegation zone after falling to seven consecutive defeats, as well as missing out on a FA Cup third-round trip to Chelsea after losing to Peterborough United in their replay.
"They probably are playing with a bit of fear because we are losing," Sheridan told the Nottingham Post. "It's hard when you're on a run like this.
"But there's only one way you can get out of it, and that's working your socks off, be brave, be strong, take whatever's thrown at you and get on with it – that's what I say.
"It's all down to the players. You've got to be brave. We're in a very vulnerable position because we are losing a lot of games.
"Before we conceded (against Doncaster in Boxing Day's 1-0 defeat), we looked quite solid and they didn't really cause us too many problems.
"But once we conceded the goal, we got a bit shambolic and calamitous, and did the wrong things.
"We made ourselves vulnerable and they could have scored one or two more.
"We're in a very vulnerable position at this moment in time. That's what happens when you're not winning games – and we haven't won for the last seven on the spin, which is really poor.
"It's not something I thought I'd have as a manager, or thought that I'd be in this position.
"It's something new to me and something that I've got to work my socks off to try to get out of."
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