I don't think you're talking about the same thing as GP. I've had spells like you describe, and I did enjoy them. And I don't know about you, but I never felt like this was expected of me by the company, so there was no pressure involved. I think that this actually being my choice made all the difference.

This seems quite distinct from what is discussed in this thread, which is people feeling some kind of pressure to work long hours, or to be available after work hours when they're supposed to be doing personal stuff. And, usually, the reasons for being called up don't seem to be some genuinely exciting problem that it feels invigorating to tackle. Instead, it's typically some form of TPS report that needs pushing around.