Although dabbing is a CRAZY experience especially to new/inexperienced smokers, it is actually really not all that different from normal weed smoking. Inhalation is the fastest method of drug intake, so whenever you smoke weed or take dabs the effects are instant. The initial onset of a weed high occurs right after you smoke it, however because there is such a high level of thc in oil, it may appear to come on much faster because you are getting that huge burst of thc. In other words, when you smoke regular weed, the actual smoke you are inhaling contains a decent amount of thc, although the majority of the smoke is from OTHER non thc combustion. However, upon taking dabs, the smoke you are inhaling has a HUGE amount of thc in it so the moment it hit your lungs it starts to absorb, so you absorb a lot more on your very first hit than regular weed. The rush you feel similar to MDMA will most likely lessen/become more distinguishable as its own feeling over time. DO NOT worry about seratonin replenishment ever with any kind of THC, because unlike MDMA it does not even begin to release the same anount of seratonin as when rolling, and will always be able to replenish itself without legitimate notable damage. In terms of actual brain chemistry, dabs work exactly the same as normal bud, EXCEPT the fact that you are just getting a BUNCH of THC at once and its all absorbing quickly. (this is the rush some experience with dabs)
Hope i helped, have fun dabbing!