Well, as for the toxins in your blood - a blood test would pick up pretty much every toxin that the cells are known to hold onto - a test wouldn't really help it would probably just astonish and confuse the haematologist. By the time a repeat test was done (within a few weeks) most of the toxins would be gone. The Herxheimer reaction is about the lymph fluid getting replenished and the cells feeling that it's safe to let go of the toxins now that the body is getting what it needs. Cells only retain toxins when it is at the body's advantage for them to do so. The Herxheimer reaction is therefore a very good sign - it means that your body is likely to make a full recovery (if it wasn't likely, the cells would keep holding-in the toxins).
After, I must confess, it left me scarred. Literally. I didn't take iodine therefore I was left with scars on my face (almost like little pox marks) due to severe iodine deficiency, which becomes even more acute during Herxheimer reaction period. Yes, I wish the vegan community was more open about HerxR but many people don't seem to want to discuss it because it temporarily challenges the idea that the vegan diet is superior. Likelihood is fewer people will try it, after all, if they get warned about a severe detox period which can last a month. So I've made it my mission to make sure, whenever I can, that others don't experience the same mistakes I made. I am fortunate that the scarring has faded and you wouldn't notice it if I didn't deliberately point it out.
But apart from the problem with iodine I felt that my body was simply much more acute. The slightest discomfort I can now feel, and I get warnings about what I might be doing wrong loud and clear. These are both distinct advantages to have - to be able to listen to one's body better. Before, especially when I had dairy in my diet, these messages just didn't seem to cut through the muck - they were dull and slow. Everything now is clean and clear and, yes, I have noticed some stability in my mood too. I have also not experienced any sickness or caught any 'local bugs' since going vegan. The only time I have ever been ill was when I failed to get a decent night's sleep for several days in a row. Or when I have actually consumed too much vitamin C which resulted in mouth ulcers - not many people seem to be aware that you can actually overdose on vitamin C.
There are mental health charities that advocate a vegetarian diet and increased fructose, so I am not surprised you are feeling more mentally agile. I suspect you would feel even more so if you increased the amount of fruit that you eat.
Hope this helps!