It accompanies the mood you're in, but it's optional to SI.
I mean, I can feel like crp the whole day but not SI, and then there were those days where I felt the same and thought, "Well, what the h-ll, let's go.."
As long as that thought or thoughts can be controlled while in that mood, the SI shouldn't be as appealing to you.

ps: It's honestly better to be in a "bleh" mood rather than a crappy one. Those blah days makes virtually everything unappealing, and those days ended my SI epoch.

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