997,528
There is no reason to believe in such a complicated theory of how life exist and how the world and universe function, the idea of nothing existing but only in the realms of thought creates way too many assumptions that must be asked. For example.
1. Why do we all see the same thing?
2. Are you suggesting that everyone but yourself are philosophical zombies?
3. Where is this realm of thought? Is it a material or a separate universe?
4. How can one comprehend themselves if they, themselves, do not exist?
5. If we are just a thought, who is thinking us?
6. If existence is just a thought, then we would need to the object thinking us would also just be a thought of another object thinking it, creating an infinite regress.
It's an unlikely scenario because of these strange contradictions, unanswerable questions and paradoxical arguments, so I deem the idea of us being simply a thought is unlikely.