Daryl Powell's side are reeling from a 58-16 thrashing by lowly Hull KR in front of their own fans last Sunday and Cunningham believes that makes them a dangerous team.
"Castleford's defeat to Hull KR was a blip for me," he said. "Hull KR had a point to prove and were in a lull.
"There's always a point when you come out of that and unfortunately for Daryl it was against the Tigers. They are also down on troops but I'm sure they will be fully fit when we play them this week."
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Powell, who has centre Ben Crooks back from injury, described his team's 11-try humiliation by Hull KR as "unacceptable" and expects a response from his players.
"Last weekend was one of the worse performances I've been involved with," Powell said. "We need a real response this week and our players are aware of that.
"Super League is a really tough and unpredictable competition this year and there's a couple of ways to go: you can put your head in the sand and sweep things under the carpet or you can stick your chest out, dust yourself down a little bit and get on with it, and the latter is what we are hoping for.
"We'll get stuck in to it, you need to be at your best against St Helens."
Saints, who gained a 28-22 win over Castleford at Langtree Park in March, got a host of players back from injury for last week's 38-34 win over Leeds and, with Dominique Peyroux expected to make his return on Sunday, Cunningham is hoping they can now start to produce their best form.
"We haven't had chance to forge relationships with key personnel because we haven't had the players together," he said. "It was the first time Theo (Fages) played with Mark Percival and had Jonny Lomax coming out of the back.
"The longer we can do that and keep them fit the better it will be for us - and the defence too.
"I need stability on the edges and whichever players do that for me will play."
Lomax, who made the headlines against Leeds with his two-try comeback from a second knee reconstruction, will get more game on Sunday time but Cunningham is determined to protect the exciting full-back as much as he can after his horrendous run of bad luck.
"It was great to see Jonny out there," he said. "He will come back to reality on Sunday that this is what he does for a living.
"Jonny gives us that extra dimension but we can't look too far ahead with him. We will look at the Cas game and then go from there.
"We have to nurture him through and look after him because the longer he stays fit the better it is for us."
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