To clear up one point: It is grapefruit seed extract, not grape seed extract. These are two different things. I use NutriBiotic, liquid concentrate. I used 15 drops, 2-3 times a day, depending on severity of the blasto.
How sick was I? I would rather have any other parasite; liver flukes, pinworms, or other, because there are definitive cures for them. I was on the toilet many times a day, had chills, could not think, work, eat, sleep, lost weight, etc. I was a wreck. Thought I was dying. Fluids went right through me. Worse than any flu.
While I was taking the Metronidazole, which is supposed to work for a lot of people, half-way through the Rx, the blasto symptoms returned.
I learned that Blastocystis Hominis is an opportunistic parasite, often latching onto a system that is already compromised by other debilitating issues such as, but not limited to, lowered immunity and candidiasis.
I was really scared and did all the research I could. I learned there was no real cure for it, (Oh Joy!) but that people felt better by eliminating sugars and starches. And a few times I gave up hope for any significant answer. Then I found Nitazoxanide (Alinia), an antiprotozoal drug, which worked. (I was willing to try anything by this time, and willing to deal later with the side effects = candidiasis, which were pretty severe.)
I could not eat one gram of any sort of sugar, fruit, dextrose, cane, beet, date... ANY! Also grains and starches. Those almost immediately initiated a reaction.
The CDC, as well you may know, considers Blastocystis Hominis a non-pathogen in humans. (I read somewhere another form of blasto is Blastocystis Ratti, spread by rodents or their droppings.) So there is not much research being done on it, or rather, not a money maker enough for labs to invest millions in R&D where there would be a big payback on distribution.
To answer your question, "Could you function day-to-day?" No, I couldn't, but I could stay off the toilet, eat, and drink without severe problems by using the Grapefruit-Seed-Extract and taking the Cholestrymine powder. In fact, if I took the Cholestrymine one day, the next day I didn't need any as long as I kept up with the GSE, though I still had a small sick knot in the upper part of my stomach, so I knew the Grapefruit-Seed-Extract wasn't going to kill the blasto. PM me if you want.