Overwhelming thoughts have a way of sneaking up on us often when we're least prepared or able to handle them.
Reason, the subconcious mind runs these old beleif programmes usually dismissed by our concious minds. However, it may only take a couple of events or triggers and these minor worries become tornadoes of swirling, impending doom, threatening to mar our very existence.
This in no way diminishes real life situations, however the mind in overwhelm cannot distinguish emotions from fact from fiction, engage in priority planning,
We often pay more attention to alarming thoughts as though by the very fear of them, they somehow become believable.