My swim coach sent us the following e-mail about trying to fake ourselves into feeling good when we are actually dying during a workout:
The goal of a "feel good" swim is to make the sensations you get on a hard set feel good, rather than bad. The idea of "feel good" is to experience the sensations you get when swimming hard in a new and non-threatening light.
When you think about it, the only thing that makes a hard set feel bad is when you think it "hurts." The sensations themselves can easily be interesting or even pleasant. When you perceive them as unpleasant, it is because you think they "hurt."
You feel them. They catch your attention. They can be intense. But they don't have to hurt or be experienced as painful if you label them otherwise and understand that there is no impending or actual biological damage. These sensations will signal biological growth through adaptation.
Experience the discomfort as something good. Make it a "feel-good" experience. Seek out these sensations. Make them happen. Notice them. Then, make a point to adapt to this new "feel-good" style in your swimming.
Wait...what? What if I am about to throw up in the pool? What if I tear a rotator cuff? What if I pass out when we're doing a set of no-breathing laps? Just pretend it feels good?
Oh. Cool. Got it.