I have the same problem.. It sucks it is so scary. These have been life savers for me SaltStick Caps, Electrolyte Pills... https://www.amazon.com/dp/B002IY96B0?ref=ppx_pop_mob_ap_share
I usually do 16:8 but am about to try my first 24 hr fast and am planning to take one of these: https://www.amazon.com/SaltStick-Electrolyte-Replacement-Capsules-bottle/dp/B002IY96B0