The first few times I tried spinning (pedalling at a higher cadence / frequency) in a much lower gear than previously - it felt, well, just plain
wrong! To keep up the same average speed (and I'm not
fast on a bike by any stretch of the imagination) I felt like my legs were going like the clappers. They weren't, of course, but that's just how it felt - quite alien to my previous grinding / trudging along.
I was knackered by the time I got back and felt much more out of breath than before, but once I recovered I realised my legs didn't feel like they'd been worked half as much and there was some "go" left in them. The more I did it, the more I got used to it, and the more I liked it - to the point where I naturally "spin" now.
It may or may not suit you - we all have our own personal style - but if it helps, then so much the better.
Cheers,
Shaun