Funnily enough, someone just asked a similar question about 'tha an fhearg orm': https://forum.duolingo.com/comment/36414690
With 'eagal' though, I feel there's a bit of a difference between them. The two examples I gave with fearg are pretty much interchangable, but it doesn't quite work the same with eagal.
- Tha an t-eagal orm. > I am afraid.
This would be used when talking about a fear that you have. Say you're home alone and you hear a funny noise. You'd say 'tha an t-eagal orm!'
- Tha eagal orm.... > I am afraid...
Perhaps some people would use this phrase interchangeably with the one above, but usually you would use it when starting a sentence with 'I am afraid (or worried)...':
Tha eagal orm nach bi i ag èisteachd. > I am afraid she won't be listening.
Tha eagal orm nach tuig e mi. > I am afraid he won't understand mi.
Am bi i aig a' chèilidh? Tha eagal orm gum bi. > Will she be at the ceilidh? I am afraid she will be.
Does that make sense? You could probably get off with using them interchangeably, but I will say that using 'Tha eagal orm' to describe a genuine emotion of fear is a bit uncommon. For that one, you would usually use 'Tha an t-eagal orm' :)
Perfect! That is clear. In fairness the examples I remember from Can Seo (Tha eagle orm) are exactly as per your excamples. Imagine a restaurant and the patron asks for soup but the waiter replies: "Chan eil bròt agam, tha eagle orm". Unless it's ectoplasm soup, I doubt the waiter is actually scared. I don't recall an example where "the fear was upon me" in an actual boot quaking way. So, your explanation absolutely makes snese.