^I really think musculoskeletal issues can explain a whole lot of symptoms.
When we're talking about that area of the neck (back of the head), we're talking about cranial nerves such as the occipital nerve - you can read about occipital neuralgia and its symptoms here
https://en.wikipedia.org/wiki/Occipital_neuralgia
Mind us that anti-epileptics (lamotrigine and friends) have been used to treat cranial nerve disorders such as trigeminal neuralgia and occipital neuralgia.
Brain zaps from SSRI withdrawal are known to be a parasthesia of the cranial nerves.
MDMA could be causing some direct effects on cranial nerve function (either by acting on the cranial nerves or acting on the brain regions that deal with the cranial nerves) and such stimulants and a long night will also be increasing muscle tension in both the neck and the breathing muscles (scalenes) that can cause issues with this region of the neck/head.
Stimulants should be increasing the tone of the scalenes, and you'll have reduced bodily awareness et cetera while there could also be some musculoskeletal/peripheral nerve inflammation after using stimulants/partying so this could be a perfect storm for some.
There was a guy who used to post a lot who thought he had contracted MS from MDMA because he had so many neurological symptoms. The night that he used MDMA he was star gazing - looking up at the sky in the worst way that you could for that region of the neck. He fit the bill for cranial nerve issues and then some.
I don't think its a coincidence that so many people are having abnormal head sensations and neck/jaw pain - this could very well all link back to the cranial nerves.
There is also evidence that cranial nerve dysfunction leads to visual disturbances and tinnitus, and there are various symptoms associated with occipital neuralgia.
Some people may be thinking "Okay there's visual snow and tinnitus from that cranial nerve stuff, but other than that its all body symptoms, and I have depersonalization and depression" - the body and brain are intimately connected. If you're walking around all day with your head feeling numb and shitty because a cranial nerve is inflamed and irritated, that's going to affect you. Also, there are brain areas intimately involved with the face and head, and the cranial nerves have something of a direct route into the brain. Every corner of the brain and body is connected in some way or another.
We also have the issue of the vertebral artery, which can be compressed in the neck and lead to xyz symptoms. But that may not be as common. Who knows.