Yes, I've been using the grounding sheet for almost a month now and can't believe how much more relaxed and connected I feel. It's the same feeling I get when I spend time in nature.

I would suspect that sleeping outside would give you the same benefits, as long as you aren't sleeping on something like a rubber mat that would block the Earth's natural current. They say that's why we're so plagued by depression and anxiety because the rubber soles of our shoes cut us off from the Earth's current. I've bought a couple pairs of grounding shoes too to wear in the summertime. After experiencing the benefits for myself I'm a believer.