Shal'tiar

Shal'tiar was a temporary state of being among Vulcans. Confronted by a problem which seemingly cannot be solved through logic, a Vulcan may enter the state of Shal'tiar, where he or she abandons logic and begins to attempt to solve the problem by any means necessary, even against logic and ethics. During this time the Vulcan in question becomes obsessive and sometimes even dangerous. 

Spock may have experienced Shal'Tiar at least once, in the 2260s. When the shuttlecraft Gallileo had nearly run out of fuel and the USS Enterprise (NCC-1701) could no longer stay to look for the shuttle, Spock jettisoned and ignited the shuttle's remaining fuel in a desperate, far-fetched attempt to catch the Enterprise's attention, and sacrificing any chance of a safe landing on the planet if the tactic failed to get their attention. Spock later stated that he deduced that logic required him under the circumstances to make an illogical decision. 

Selar entered Shal'tiar after encountering Rulan 12, and becoming desperate in her attempts to find a way to save her son, Xy. She was contacted by an alien who instructed her to capture the baby Cwansi and bring it to an uninhabited planet, which she did, incapacitating Robin Lefler and Soleta in the process.