I can get that panic feeling when I’m extended fasting too. For me it’s the hardest thing about fasting. I’ve heard fasting can alleviate anxiety, but I haven’t really had that experience personally. My fix is as others have suggested; electrolytes. But I have broken a fast before too because I’m panicking too much. I’d be interested if anyone has discovered any studies or clinical papers about the correlation between fasting and anxiety.
Its a good idea to take electrolytes like pink Himalayan salt or sea salt and water before starting a 72 hour fast. Avoid white table salt as it has caking agent and not all electrolytes. Whether you can bring the deficit around at this point you will only know. Try loose leaf green tea for mood and fat burning. It helps my fasting tremendously.