Myths were created as an oral tradition. Some myths started out as revaluations or dreams some were even true stories, then they morphed into some grandiose story.

You can set one anywhere in your dreams, Leprechauns are stuff of myths, folk law and fantasy so your only going to catch one in your dreams.

There aren't any myths to tell us what Artemis dreamed of, so no one can say for sure.

No, dreams are not caused directly by excess hormones. Dreams come from our minds, especially from the subconscious mind which uses images from our waking lives as well as images from myths, traditions and many other sources. However, chemical imbalance in the body can be one of many factors that effect one's dreams.
No.

Some unusual life after death myths include the fact that everyone hears from their deceased loved one. Another is that after death communication only happen in dreams.