If you don't know you're going down, you might think you are upside down and going up. Disorientation is a strange thing.

In addition to what huslage said, there’s something called an aerodynamic stall: in very oversimplified terms, if you go up too steeply without adequate thrust your wings will produce dramatically less lift all at once.

Or even worse, and more likely, just one one side (wing drop). Then you're really doomed. Happened recently on an ATR I think.

I did some flying with a hood - no ability to see outside but I could see instruments. It was uncanny, and I got totally disoriented.

The only thing that saved me is that as a former sim jockey I was used to flying just on the instruments and I knew it was very unlikely that they went wrong just as I was flying blind. So I focussed on the instruments and ignored the feeling that the plane was literally flying on its side.

It is very unsettling.