Questions on fasting

1. Can I take Tylenol for my headaches while fasting? (I’m talking about when I’m going more than 24 hours with nothing in my stomach)
2. Is there any indicator that I should be aware of that means I need to “stop” the fast? (As in I’m going to die) I realize I will feel like ass, but im just looking to give myself absolutely NO doubt as to why I should quit once I start.

Thanks so much!
Thinking about doing it again. This time 3 days rather than 2. 🤔🤗👹