The Imps have dropped to fourth in League One, two points behind the Black Cats, following a run of just one win in seven games.
Lincoln suffered a 3-0 defeat at home to Gillingham last time out, yet Appleton is trying to stay positive.
“The lads are fine. In football for me, it’s all about the next game,” said Appleton after the Gillingham game.
“We weren’t going over the top when we were winning every week, no-one was getting carried away with themselves. We were enjoying that moment and rightly so, because the performances were good.
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“If you take the last four games, three of the performances have been pretty good, yet we’ve only taken four points from them. Over a period of time, that will change.”
On Sunderland, Appleton added: “Everyone will be expecting them to turn us over.
“We’ll go up there and enjoy it. No-one is expecting us to win, everyone is expecting us to lose. Maybe we’ll surprise one or two.”
Lincoln recently lost to Sunderland on penalties in the semi-final of the Papa John’s Trophy, yet the performance encouraged Appleton.
Black Cats striker Charlie Wyke scored the equaliser that day, while Appleton also believes Lincoln striker Vadaine Oliver can cause problems.
“We played well there that night,” recalled the Lincoln boss. “Clearly, Charlie Wyke is a presence and a danger.
“Him and Oliver are probably the best two in the division of, when the ball is around them, dealing with it, getting the flick-ons and bringing other people into play.”