while going beyond expiration date for tablets is less of a risk vs for example capsules or liquids i would strongly discourage ingesting, inhaling, injecting etc etc pharmaceuticals 20 yrs past expiry.. they do degrade over time and physiological effect of those degradants may not be known - stability studies to support shelf life do not run for 20 yrs

but in OP issue unless you chew on your mattress that is less of a concern there...