I tried looking around, but couldn't find any topics with this theory, so I figured it might be an interesting first post. I will here try to give my theory for the mechanism that makes healing, in general throughout the cosmere works, and hopefully back it up with some good sources.
Statement 1: Physical healing (at least the ones I will talk about, e.g. F-gold & stormlight) heals by making the physical body adhere to the Spiritual ideal.
Statement 2: Spiritual healing works directly on the spiritweb, and there is no ideal for the spirit to adhere to, and must therefore be a different mechanism.
Statement 3: Forgery instantly affects the physical, by causing it to adhere to the Forged Spiritual ideal.
Statement 4: The body can be changed without changing the Spiritual ideal. (This is obvious because the body can be damaged and then healed back it's unchanged ideal)
Statement 5: Time does not exist in the Spiritual Realm.
Statement 1 & 2 I will only use to remove Spiritual healing from this theory, as my proposed solution would not affect the Spiritweb.
Statements 3 & 4 together show that static spiritweb without external influence does not affect the Physical aspect, while a changing spiritweb does affect the Physical aspect. This makes me to come the conlusion that:
A static Spiritweb does not filter down into the physical, but a changing Spiritweb does.
Using this concept I believe that physical healing works by "rippling" the Spiritweb. This causes the Spiritweb to change, as in not being static, but it doesn't actually change any of the information contained in it. By rippling the Spiritweb like this it forces the Physical aspect to adhere to the Spiritual again, and a stronger ripple would result in a faster healing. The reason Forgery looks instant would be because the change is severe enough to count as a very large change, and cause the Physical to update quicker.
Since time does not exist in the Spiritual Realm, the only way for things to change is through at direct causal chain. In other words things can't change (on their own) or over time. Therefore the only way to cause an update in the Spiritual realm is to directly start a causal chain from the Physical Realm, where time does exist.
I've included what evidence for I could come up with, but there are some other explanations that could also explain it. The side effect of each magic could simply directly cause these things to happen. Gold could simply "look at your spiritual, and then change the Physical to match it", rather than go through the extra step of starting a ripple in your Spiritweb.
Since every time the Spiritweb changes, there is some cause, proven by the fact that time does not exist in the Spiritual Realm, means that we don't, and likely never will, have a case where the Spiritweb constantly changes without some external cause. And this would really be the only way to prove or disprove the over-arching theory, as the static Spiritweb part is proven trivially.
Thank you for taking the time to read this theory, may the ripping-it-to-shreds begin.