Is the contamination of clothes and items placed on a wooden table, after suspecting a najāsa (ritual impurity) has fallen on them, considered a waswasa (whispering from Satan/obsessive thought) that should be ignored, or have they actually become impure?

We warn everyone afflicted with waswasah (whispers/obsessive thoughts) against giving in to it. Rather, one must turn away from everything it presents. Nothing should be considered to have exited unless there is certain conviction upon which one can swear an oath. The default is that nothing has exited unless its exit is certain. If the impurity's exit is certain, but there is doubt about it having stained the garment, then the default is that it has not stained it. Impurity does not transfer merely by doubt. The thought that impurity has transferred to everything on the table is waswasah. It is not obligatory to wash clothes except for what is known with certain conviction to have become impure.