This seems odd, but whenever i do repetitive work on my pc, i'll usually have vivid dreams of still working and wake up with a severe migraine & nausea?

Classic finding: The early psychoanalysts, who paid attention to dream content, noted that people who've spent much time the previous day doing repetitive tasks often dream of them vividly. I've not heard of this as a migraine trigger, and would be interested to hear from a neurologist. Most migraine can be managed fairly well nowadays and i hope you are able to get relief.

Chances are...: ...That though repetition is a key form to trigger a reaction, the content is important, too. Probably some content triggers dreams (and migraines) while other content does not (or is less likely to). What you describe has many similarities to "trauma:" responses--though here i trust "trauma" is too strong a word. In short: something you are doing gets "under your skin". Try to find what.