The poor grade of elastic used in today's bedding is sub-par compared to American manufactured goods made back in the day. FYI - using bleach deteriorates the integrity of the rubber in the elastic.
Do I eat this week or buy another set of sheets? Never fear, food will be on the table and you will no longer "wear" your sheets while sleeping.
I suggest you or a trusted seamstress add a fresh stretch of elastic around the perimeter of your beloved fitted sheets. Sweet sleep with your newly fitted sheets!