This is part of it, and days two and three are reliably the worst of the whole thing. Every symptom you have listed is your body clearing out rather than reacting badly to the vape.

The cough first, because it alarms people the most. Your lungs are lined with tiny hair-like structures called cilia, and cigarette tar paralyses them. Within 24 to 48 hours of stopping they start working again and begin sweeping years of debris upward - which is what you are coughing up. It typically peaks around day three to five and then drops away quickly. The extra phlegm is the same process; drink plenty of water and it passes.

The headache is your carbon monoxide levels normalising and your blood oxygen improving, and it usually goes by the end of week one. The broken sleep and vivid dreams are your nicotine metabolism adjusting - nicotine is a stimulant and your body is recalibrating when it gets it.

One thing worth checking, because it is the fixable one: if the headache lands specifically in the afternoon, you may be undershooting your nicotine rather than detoxing. Vape more freely and see if it lifts. Conversely if you feel light-headed, take fewer puffs per session - but do not stop vaping altogether, that is how people end up back on cigarettes. Day-by-day breakdown is in the first week after quitting guide.

The cough got me too and I genuinely thought the vape was damaging my lungs. Finding out it was the cilia waking up and shifting the tar reframed it completely - it went from frightening to almost satisfying once I understood what it was.

Mine peaked on day four and was gone by about day eight. The vivid dreams hung around a bit longer, maybe a fortnight. Both stopped without me doing anything about them.

Day three to five peak matches me exactly. And the afternoon headache thing is interesting because I have been quite restrained with the vape, worrying about overdoing it. Going to stop rationing it and see what happens.