I have not tried ivermectin but I have used pyrantel pamoate and I had a similar feeling from it. Pyrantel pamoate works by paralyzing the nematodes that come into contact with it. This is because it inhibits the function of the nerve tissue of the muscles of the nematode. Pyrantel pamoate largely stays within the human digestive tract because it is not absorbed well. However, some of it is slowly absorbed into the bloodstream. This has a similar (but much milder) effect on your body. You may notice your breathing becoming harder and your heartbeat becoming faint. This is what happened to me when I took it for a roundworm infection. After a while the feeling went away and I was fine. However, if the symptoms persist or are more severe, contact your doctor.
The die-off may also make you feel weird. For me, the die-off made me extremely tired and fatigued. Remember to drink lots of water.
Also, there are some vitamins that help your body metabolize the dead parasites such as vitamin B2 which may help. I would not recommend taking niacin for this, however. Niacin is harder on your liver, especially if you have massive die-off. Niacin breaks dead- parasites down into end-products that in high concentration can be bad for you (such as uric acid)
But above all, drink lots and lots of water to help your body flush itself out.