We have a bit of conundrum with the Moon. It's usual interpetation often has to do with hallucinations, insanity, wildness...but it also relates to dreams, fantasy, artistic talent, creativity, psychic ability, romance. This make interpeting the reverse a bit troublesome. Is it positive or negative? Let's see what we can work out.
1) Opposite: trying to figure out the opposite of the Moon is problematic. Logically, it should be "The Sun." But we already have that card. So let us say, instead, that it is the "Dark of the Moon." In this instance, I would interpet the Moon at its very worst, giving it's milder interpetations to the upright.
By the light of the Moon, we can still find our way--even if wild things do happen by that light. When the Moon is dark, however, dark things happen. We might well say that things are not merely wild, but primitive. Criminals lurk in the dark, shady folk with dark purposes and intents. Sexual predators instead of romance, artistic talent used to hurt and destroy. Evil fantasies and dreams. Here is the stalker, the person who wants to scare and harrass.
This interpetation would probably include a bad psychological time. If the querent suffers from any problem or has someone in their family suffering through such a problem (depression, bi-polar, substance abuse) they are going to be going through a dark time with it. It's going to be a long dark night of the soul.
2) Blocked: The energy of the Moon is that of chaos. It can be insanity or artistic genius, but either way, it is unrestricted. Blocked suggests a writer's block, perhaps a sexual block, even a block put on that insanity (medication that dulls the mind?). The block might be physical (bars on the window!), or just self-restraint. This is not order, so much as a lock on the door, keeping Chaos/freedom/wildness outside.
There may be calm with this blockage--but it is artifical. The chaos (insanity?) has not been removed/erased/corrected, only prevented. Bars protect the person from the wild, but the wild still calls to them. So, in this case, crime is prevented, but not stopped. Depression, etc. are held off, but not cured.
3) Upsidedown: Turn the card upside down and the creatures are not gazing up at the Moon--the Moon gazes up at them instead. This suggests that what rules and commands the wild is no longer in charge. Base as these intincts may be, they do have a guiding light that they look up to, a gut feelingthat they are following. It's certainly topsy-turvy for the light to be looking up at them, for them to be in charge instead.
It is out of primodial ooze, out of chaos, that order comes (the Sun will follow the Moon), but upsidedown suggests that order is moving into chaos instead. That even the guiding light of the moon has been subjected, and only the primitive reigns--unchecked, directionless, with no purpose or hope of coming to an end.
This is the sort of interpetation one might find for revolutions and riots, for countries melting down into political tormoil with no path to peace in sight. On a more personal level, you're likely to get this interpetaton for a complete mental breakdown or a merciless plummet into the worst depths of drug addiction. There is no civilization. Men and women are ruled entirely by their animal natures. Complete anarchy.