Forest were chasing a club record-equalling seventh straight win but it looked like manager Billy Davies would taste defeat for the first time in eight games when Will Buckley put the visitors back in front with five minutes remaining.
Poyet though had sympathy for the goalkeeper and said: "To begin with I thought the shot must have taken a deflection but when I've seen it again I nearly killed myself!
When you are a keeper you pay the price and Casper has done that today. He was having a very, very good game, making two or three good saves, coming for crosses and kicking very well.
More top news
Simon's Blog - Bird Watching
A British soldier will not be prosecuted over the death of a comrade from West Sussex on an Afghan battlefield four years ago.
Monday night's forecast for the west of the region