My thoughts are that it is either cannabis sativa (as traces of cannabis were found in bowls used in the Eluysian Mysteries in Ancient Rome) or ergot (which is a very similar chemical to LSD, and which grows on barley). Based on some LSD and cannabis edible trips I've experienced in the past, I can relate to the "we have become immortal, we have gone to the light, we have found the gods" feeling. It can create a feeling of being one with the Supreme Consciousness and make you realise that this "I Am" or Atman, is immortal. I would think it's more likely to be cannabis purely because sativa cannabis edibles can make you feel energised and want to dance, while LSD like substances make the body feel alien and often don't want to dance.