Ytdyklly

In the episode "Fusion", when Tolaris does the mind meld with T'pol, she resists, then submits. But, the emotions seem overwhelming.

Memory-alpha says

Another side-effect was the transfer of emotion. When Spock melded with James T. Kirk of the alternate reality, both seemed emotionally affected by the experience and Spock apologized, explaining that emotional transference was a side-effect of the melding process. (Star Trek) Indeed, melding created a strange sense of euphoria in the participants. (TOS: "Dagger of the Mind")

So, was she affected by the emotions of Tolaris, who seemed pretty agitated/excited? Or was it her own emotions that overwhelmed her?

In other Star Trek series' mind meld is shown as something Vulcan's seem to know a great deal about. While, T'pol seems ignorant of it. Is there a back history of how mind-meld became common?

I am watching the series for the first time. Will look into links, not minding spoilers.

If you're watching Enterprise for the first time: just keep watching.

If you don't mind spoilers, then the Wikipedia article on T'Pol
(emphasis mine) explains it pretty well.

T'Pol, who is described by her superiors as a maverick and a rebel, became fascinated with Tolaris, a member of a group of emotionally free Vulcans encountered during the first year of the Enterprise's mission. Tolaris introduced her to the concept of the mind meld, which at the time was considered a taboo activity among Vulcans. She severed her relationship with Tolaris after she asked him to stop the mind meld and he refused, attempting to continue the meld without her consent (essentially a form of mental rape), and causing her to forcefully break the link. She later learned that she had contracted Pa'nar Syndrome from the encounter. This condition was kept in check with medication. In 2154, T'Pol, who had been told that Pa'nar was an incurable virus, learned that the condition was in fact caused by an improperly trained melder, and contrary to what the intolerant (and soon to be overthrown) Vulcan High Command had decreed, it was indeed curable by the touch of an experienced mind – provided to T'Pol by T'Pau.


T'Pol was told that she is genetically incapable of initiating mind melds herself, however following the 2154 overthrow of the Vulcan regime that stigmatized mind-melding she learned otherwise. She performed her first mind meld upon Hoshi Sato, with the assistance of Jonathan Archer, who had learned details about mind melds during a period of time when he held the katra of Surak.