Yes, definitely! I think some hormonal and metabolic things can happen during a fast in the short term that can make people feel rather energized (you could see how an adaptation like that could energize you to go out and find food). But the starvation phase of this study was six months. So it's quite possible the participants did feel great the first week. But too great a deficit for too long is definitely not going to make a person feel great, and the body also changes in ways that are seemingly detrimental to health.