I am sure you must be panicking right now. When the body has such a sudden almost violent reaction it throws you off, and makes you want to quit. I would say stick it out, just stay down, and stay calm. Try relaxing your body sequentially, or relaxing in a hot bath. Depending on your stats (age, weight, health history etc.) this could be your first rush of detox. The first time i water fasted it was around day six, that i had a somewhat similar reaction. I had been trashing by body for a long time with booze, cigarettes, and often prescription medication. It was a really rough night, and i literally felt like i was going to die; i was sweating bullets, convulsively shaking and my head was throbbing and there was this whooshing sound in my ears. I ended up taking a hot soak in the tub, calming down and then i slept for about 9 hours. The next day i felt much better, and two days later i felt great. Detox is not pretty, it is basically all of the stored toxins in your fat, that your body didn't fully process in round one, that are hitting your blood stream / system now. Just know that it happens but that this means your body is healing itself and the fast is working. If it persists for longer than a day, or if you sleep and it continues I cant honestly say what should be done. Good luck, and take it super easy!
Congrats on making it to day 4! you are actively healing your body and you should be proud of your accomplishment!