[devanti]

Don't worry about it.

He's trying to motivate his employees by showing his dedication. If he wants to work in the middle of the night, let him do so. It's normal for startup founders to work late or wake up in the middle of the night with random thoughts.

I highly doubt you're expected to respond to it immediately anyway.

Also, it's not really your job to worry about his cognitive capabilities. That's his responsibility, and some people can get away with less sleep than others.

If you don't trust in his ability and the future of the startup, then you should simply leave the company.