Laura,  Your first example uses lackadaisical in the manner that I would use it.  For your second and third examples, I would use the word "lethargic".   For the most common usages, "lackadaisical" describes an attitude or approach to something  while "lethargic" describes a physical state of being.

Examples:

I have a lackadaisical approach to learning Spanish grammar.  I study things as the mood strikes me.

I am taking a beta blocker for my high blood pressure and it is making me lethargic. I don't have the energy to exercise.

The origin of the word

Alas, alack, there are times when life seems to be one unfortunate occurrence after another. We’ve all had days when nothing seemed to go right. When folks had one of those days back in the 17th century, they'd cry "Lackaday" to express their sorrow and disappointment. "Lackaday" was a shortened form of the expression "alack the day." In the mid-1700s, "lackadaisical" was coined through addition of the suffix -ical. The word lackadaisy also was used around that time as an interjection similar to "lackaday," and this word, though never as prevalent as "lackaday," might have influenced the coinage of "lackadaisical."

Additional Meanings:

- lacking vitality and purpose

- lazy or idle, esp in a dreamy way

- acking enthusiasm and determination; carelessly lazy.

Examples:

- Failing to use anti-virus programs is a lackadaisical approach to protecting your computer.
- Feeling particularly lackadaisical in the summer heat, they lazily tossed a ball back and forth