Huh...
I guess I'm the odd one out here. I wear my PJs for an entire week, and swap them out when I do my laundry. Exceptions being - it's hot in the house and I was sweating during the night. Or it suddenly got hot and I want lighter PJs. Or, it suddenly got cold and I want my cozy flannels. Or I spilled something on myself while making breakfast. Anything like that, I'll change my PJs.
I actually change my undies twice a day, though. I like to sleep in a fresh pair, and I always want new ones in the morning. I couldn't cope with wearing the same ones two days in a row!
My pjs are just tees and shorts/pants.
When I'm travelling for eight days, I only bring one pair of PJs, and just ten pairs of undies. (Which is a sacrifice for me.

)