Can't go more than 52 hours

I've (M25 140 lbs 5'7") been doing 24 to 48-ish hour fasts for about a year now and I cannot for the life of me get past 52 hours without feeling absolutely horrible. I supplement with magnesium pills (500mg) at night, 1 tsp of salt, and 1/2 tsp of nosalt (for potassium) over the course of each day.

After waking up on the the third day I start feeling extremely sick and nauseated like I'm gonna pass out and/or throw up. I end up breaking my fast with some eggs then I sleep for about an hour and quickly feel better.

Is this what keto flu feels like? I'm not on a ketogenic diet but I'm still losing weight after a 40-ish hours fast once a week. Any advice is appreciated.