I found that when I used my Macbook with an external keyboard and mouse that I still had problems. Unplugging it from the charger helped, but then it wouldn't last very long on battery. Hooking it up to an external LED monitor and moving the laptop as far away from me as possible helped me the most. So far I've found I can't tolerate monitors that are larger than 20 inches for very long. I was prepared to go down to 16 inches, but it hasn't been necessary. If you go this route I would recommend you get a monitor that is flicker-free like an Asus or ViewSonic. Are you able to hook up an external monitor to the iMac and then place it further away from you? The monitor I sit in front of runs under 10 watts, but the Macbook runs at 50 watts and up so it makes a big difference having the main offender further away.
Did you ever try the biomagscience magnets, Elle? I've found wearing a magnet helps with that sticky-blood feeling. The first few nights trying to sleep with it I could really feel a strong increase in circulation. They have a little section on magnets and rouleaux formation here
https://biomagscience.net/prevent-heart-attack-and-stroke-while-supporting-health-and-wellness/One thing I've also found that help with this are negative ion generating pendants, the ones made from lava and tourmaline and generically known as "scalar pendants". There is some concern that these put out very small amounts of ionizing radiation. Both the ionic output and radiation are measurable, so try at your own risk. I've kept a tiny one on me for several years.