But is it hard or hard work? I would think that is different. A lot of things which are hard to do, are not necessarily hard work.

Completing a level in a computer game can be extremly hard. Yet I would not call playing a hard computer game, hard work.

I am not trying to minimize your efforts here. I am just trying to get people to reflect on the difference between putting in a lot of time and effort into work you enjoy greately vs doing work you hate.

If the job is hard but enjoyable, then it is not a sacrifice the same way as say cleaning toilets or carrying carbage is.

Of course I accept that how it feels depends on the day. Sometimes our brain is just not up for complex mental work. Solving a challenging problem is not fun at all. It might be even described as a terror as you say. Especially if it is hard while you have a short time limit and is stressed out of your mind. In those case, YES you are definitely doing hard work.