How did I wake up without my panties on?

Few years ago, once at a summer season, after taking a shower I went to sleep and fall asleep wearing a skirt and T-shirt and when I woke up around 2 am, I went to take water from the fridge then I realized I was not wearing any panties underneath...I looked for my panties, but I did not find anywhere near my bed.

I usually used to remove my bra during the sleep if I would feel Hot in summer seasons but never removed my panties by myself.

I wonder, How I woke up without my panties?

I had My mom-dad and one of my sister at home and my sister used to share my room with me.