About ten years ago, I experimented doing 20 minutes in the morning and an additional 20 minutes in the early evening. I did this for about six months, and I may have overdid it, because some very, very strange things began to happen. I stopped meditating after a particularly weird and frightening experience which I will now describe:
I was entirely stone cold sober, driving my car on the highway talking to a friend in the passenger seat, when suddenly I found myself looking down at the planet, from what I can only describe as an orbital altitude of somewhere around 400 km or so, while at the same time, I continued to drive the car and have a discussion!
Part of my consciousness (or perception) seemed to momentarily bifurcate and be somewhere else, in this case, floating high above the Earth. That was the day I stopped meditating. Apparently this is a known attainment in certain circles that believe in this kind of thing (I'm still a skeptic at heart) but being in two places at once wasn't my cup of tea. I have a hard enough time as it is focusing on the road in front of me!
I wouldn't say this is the only strange thing I experienced; there's a lot of them to speak of, but that was certainly the strangest of them all. I've taken much more pleasure and satisfaction from lucid dreaming instead, which is something I still do to this day.