Here are two sentences containing both the plural and singular forms.
- "Fred faced a nasty ordeal at work, and needed to relax by walking through the park afterwards."
In this case, it sounds like Fred had a single difficult day at work, so he decided to walk in the park (with the added implication that he doesn't always do this). Perhaps the electricity went out on the busiest day of the year.
- "Fred faced nasty ordeals at work, and needed to relax by walking through the park afterwards."
Here, it sounds like Fred regularly had difficult days at work sometime in the past (implying that something changed in his work routine), and so he would also regularly take relaxing walks in the park (but, again, no longer does this). Perhaps he used to be a mail man and was chased by dogs regularly, so one day he decided to apply for a transfer to desk duty, or quit for another job.
Here's a different example:
- "Fred faced nasty ordeals at work today, and needed to relax by walking through the park afterwards."
In this case, "today" (could also be "one day," "another day," "last Friday," etc.) makes it so the sentence means that Fred faced multiple ordeals in a single day. For example, he could have been late because of a flat tire, spilled coffee on himself before a meeting, and had an employee get sick at a crucial moment.