Nothing else has changed about my campaign. I know it’s possible that there was suddenly more demand for my keywords and it’s just a coincidence but, well, doubling my cost causes havoc for our business. My bid strategy is set to maximize conversions. Any advice?
A step change (e.g. stopping a campaign insistently and then instantly relaunching) could cause performance to diverge;
(you diverted the system out of its “steady-state.”
Now, you should slowly, gradually, optimize. It will take days. Do no make “sharp” changes.