I had a very powerful experience with a small piece of Moldavite. A few days after I obtained it, I decided to work with it a bit. I held it in my hand for about a minute, whereupon I felt such a strong sensation of being rocketed out of my body that I had to put it down. For the next 36 hours, I felt spacey, ungrounded, jittery, and as if I weren't really "here".
After I began feeling like myself again, I noticed that my perceptions about some things were different. For example, when listening to music, extremely vivid moving pictures would appear in my mind. Also, one evening I clearly saw my dog Zorro, who had crossed over several months earlier, as if he were standing right in front of me.
Thinking it over aftewards, I feel what probably happened was that it raised my vibration very suddenly and unexpectedly, which was quite a startling experience, but overall a good thing. I definitely wasn't prepared for it, and if I had it to all over, I would, but I would make sure I didn't have anything important to do for the next couple of days, because although I could do my scheduled readings just fine, I felt a bit ill at ease when I had to interact with people. I just felt very "raw" and uncomfortable in my skin for that period of time.
After this experience, I was a bit hesitant to touch the Moldavite crystal again, but I found that it was apparently a one-time thing.