Your metabolism slows down significantly during deep sleep cycles. Of course, metabolism rates in general differ amongst individuals but if you have issues with fasting, it would "likely" indicate that you have a faster metabolism rate. If you're planning on sleeping through the fasting period, I'd suggest you increase the fasting period from the recommended 8 hours to 12-ish. Have a light meal with carbs and no protein [protein takes longer to digest] 4-ish hours before and sip on cold water if your stomach feels empty. Carbs digest rapidly, so if you go to sleep and wake up 6-8 hours later, it'd be safe to assume that you'd have an empty stomach. Also, take into account that since the SN regimen requires you to take antiemetics, you're likely going to have to wait a little bit longer after waking up on an empty stomach. Cold water's your best friend, but do not drink a lot of water, only tiny little sips. Too much water will 100% make you throw up.