Regression fallacies offer an explanation as to how an ineffective treatment can seem to work due to random fluctuations of symptoms. Very similar to this idea is the body's natural healing process. While regression to the mean explains that a person perceives that a treatment is working while overall their condition remains unchanged, with natural healing or additional treatments the body may actually be getting better but not because of the new treatment.
The body is a natural healer. A cold, for example, will go away on its own without any over-the-counter or alternative treatment. More serious ailments do require treatment and it's likely that patients continue with conventional treatments while desperately trying whatever 'alternative medicines' they can find. For example, a cancer patient may be undergoing standard chemotherapy and radiation treatments when they decide to add a new cancer fighting tea blend to the mix. The cancer goes into remission. Which gets credit - the chemo or the tea? It's the most dangerous of quacks who advise against conventional treatment while peddling their own cures. Lifestyle changes can also be included with additional treatments. Someone complaining of fatigue may change their diet and begin exercising more while also taking their favorite algae supplement. The end result may be an improvement, but the reason is unclear.
When it comes to quacks and pseudoscience, all three of these scenarios - natural healing, additional treatment and lifestyle change - can lead to positive testimonial: "I took treatment X, and my condition improved." The reality is that the statement may be true but that doesn't mean that 'treatment X' is the causative agent for improvement. Evidence based medicine relies on appropriate controls (placebo, existing treatment) and large sample sizes to separate treatment effects from other reasons for improvement.