No, you're not hallucinating; you really are seeing bright green mushrooms, but if you are partial to the odd magic mushie, these images won't faze you in the slightest.
These neon green mushrooms, or Mycena chlorophos, to use the technical term, emerge during the rainy season in Japanese and Brazilian forests, scattering the floor with glowing spores. The bases of tree trunks, fallen branches, leaf litter and moist soil provide perfect breeding grounds for the mushrooms.
Found mostly on Mesameyama island in Ugui, Japan and Ribeira Valley Tourist State Park, Brazil, the appearance of these garish looking fungi is due to bioluminescence, one of the weird but wonderful reactions that happen naturally in many plants and animals.
Bioluminescence occurs when the natural chemical energy produced within an organism is converted to light energy. The result is an amazing display of natural fluorescent light, or 'cold light' (as opposed to red hot light). The color of bioluminescence is normally at the blue/green end of the visible light spectrum.
This organic light display can be seen in the late summer months, and although there are nightly visits to the forests in Japan, these rare shrooms only thrive where they are because they've been relatively undisturbed by humans. So, for now it's probably best to enjoy them from the comfort of your own home, that way they'll be around for a while longer. And, no, you can't get high on them, although no doubt someone has tried!