Saturday's game at King Power stadium ended 2-2.
Castagne told the club's official site: “We can't give them easy chances and goals like that. We have to be tougher. The Premier League is not easy, but I think we're shooting ourselves in the foot in the last few weeks, so we have to get back to our form.
“It's definitely two points lost. We have the same ambitions as last year. We want the three points against every team and, especially at home, we have to do a lot better.
“We'll work on that. As I said, we need to find our form again, and then we'll maybe get some wins in a row and get going.
“We've seen glimpses, but it's not like last season. We have a lot of things to work on. We have to say, we created some chances, but it's difficult. I'm never satisfied and I think the whole team can't be satisfied with that."
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