The creative process can be much like a rollercoaster. Up and down and up again in no time. It's impossible to avoid these emotional curves, but what you can do is identify them and fight back.
Teams' energy is contagious. When a member starts being passive or distracted, it's easy to end up with a unmotivated group. The Same thing can happen when someone brings good energy to a team that feels paralysed.
Good team players and leaders can read the energy of the room and contribute to moving it towards the one needed at that stage of the process.
It's not an easy task; there are several complications here:
Reading the room
When you make your assumptions, you can fail and cause wrong interpretations. And if you ask, people might not answer you sincerely, or they might not even realise themselves what the situation is. Run reflections with your team, look for signals and, in any case, speak for yourself. If you feel you need energy, just bring it or ask for it.
Identifying the need
Not all stages need the same kind of energy. When ideating, you want the team to be at a high level, but you won't need that when filtering ideas or when researching. Staying on top all the time is not practical, neither realistic.
Changing the mood
Finally, let's say you read the room correctly, and identify the need for the situation. How do you change your team's energy? Imposing will only create frustration. You should start by being an example yourself and hope others feel moved.
The task takes a lot of effort, empathy and emotional intelligence, but it can make your team reach the next level.