I can voluntarily vouch for both items as PJ's. My Better-half have used both from time to time & I have used sweats on and off all my life. The last few decades I have used them as "fever turbo boosters," if I'm sick I'll *nuke* that bug outta my system by super heating with sweats and extra blankets. It's always worked for me....I am usually never wrong.
I'll let K dog win this one.
Yoga pants or sweatpants can be pajamas.