There are some things are genuinely physical. Here is an example: Marijuana is known to constrict the vessels of the brain. Over the long term, the brain compen

There are some things are genuinely physical. Here is an example: Marijuana is known to constrict the vessels of the brain. Over the long term, the brain compensates for this to return the vessels to a normal state. When you suddenly stop smoking cannabis routinely, the vessels expand because the THC is not maintaining their restriction. Expanded vessels in the brain are a common suspected cause of migraines, and severe headaches are a top reported symptom of cannabis withdrawal. Interestingly, this effect of cannabis on the brain's vascular system also makes it a highly-researched drug for migraine treatment. It would be like taking migraine medication every day for a long time, then suddenly stopping and getting a flood of headaches as the brain re-adjusts. Now, I don't think this is "psychological."