Instructional Designing vs. Technical Writing (degree, jobs, pay, small business)

[Wordsmith12]

This question goes out to aspiring/seasoned professionals in said fields, as well as those who might have any knowledge on the topic:

What are the main differences between instructional designing and technical writing?

I am trying to zero in on writing-heavy jobs that would allow me to earn a decent living. Though my degree and experience thus far have been in marketing (website copy/editing) for small businesses, I would love to find something in higher education/curriculum without having to stand up in front of a class and teach. That's precisely why I've thought about working at a university. I've read about instructional designing but honestly have no clue as to the field's pros/cons, let alone what skill set is typically required of IDs.

I've also heard that technical writing positions tend to be boring but pay well nonetheless.

For people who simply prefer to write, which might suit them best -- copywriting/web editing, technical writing, or instructional designing?

Any comments/suggestions welcome.