I'm feeling very sleepy. Can I sleep for more than 8 hours also?

It is absolutely normal to feel tired or weak than usual during a 3-day fast. As your praanshakti is fully engaged in cleaning, there is not enough praanshakti left for other tasks, and hence we feel sleepy.

Make sure you give your body rest when it asks for it. There are four types of rest through which the body can get abundant sleep, rest and relaxation-

Physical Rest
It is important you get sound sleep at night. Please go to bed early. The maximum healing happens during 9 AM and 12 AM. If you face any detox symptoms (fever, vomiting, diarrhoea, weakness, laziness, nausea) please take rest in the afternoon as well. Also, avoid very heavy exertive workouts during a fast. Instead, do light yoga or brisk walking.
Sensory Rest
Overusing gadgets such as computers, laptops or mobile phones causes harm to our senses. During a fast, it's not only important to give rest to your body, but also to your 5 senses (sight, hearing, smell, taste & touch). Apart from the webinars, avoid using your mobile phones or computer screens.
Mental Rest
Fasting is absolutely useless if you're doing it in a state of stress, tension, anger, hatred, distrust, discontent, greed or violence. It is very important to give your mind also rest while on a fast. Bring your mind at peace by chanting, meditation, listening to kirtans, worshipping, associating with good company and studying the scriptures.
Physiological Rest
This means giving rest to your internal organs - your stomach, pancreas, intestines, liver, gall bladder, etc. When you stop eating, the workload of these organs is automatically reduced, thus providing physiological rest.