Ergk….your guesthouse has dirty pillows? Dust mite allergies? Double up on your pillowcases at a new spot. Place each case on the same pillow in opposing directions. This means, the opening on Sir Pillowcase may be on the leftside, while the opening of Lady Pillowcase may be on the rightside. This helps to prevent any bacterial, mite city skankiness from escaping via an open pillow slit and straight onto your face. Your sinuses may thank you in the morning.
Not working for you? Sew a lightweight zipper at the end of a single case and use it as a liner. For those times you don’t use it on your pillow, it can double as a laundry bag to wash delicates, or as a soft laundry bin (on short trips).
Or if you really want to be proactive, buy a zippered pillow liner before you skip.