I don't think you overdosed
In my opinion and from my experience, the sensations you are having are not abnormal. You will experience many things which may cause you to feel fear before you win this battle.
I have followed ICU's protocol and taken albendazole and ivermectin together without harm. If I recall correctly, you will take fewer days of ivermectin after the 1st week and the problem will resolve itself.
I did not personally experience nausea. Because we all have a different mix of parasites, located in different parts of our bodies, no one will have exactly the same experiences.
I do recommend you drink plenty of water to help with the detox of dying parasites. Also, the most important thing is not to let yourself become constipated. Do whatever it takes, castor oil, laxatives or whatever. This is against ICU's protocol, but feel constipation is Enemy #1.
You should try to remain calm and hang in there.