In 1989 someone asked the Rebbe whether or not Lubavitcher Chasidim say Tachnun on Gimmel Tammuz and Chai Elul. The Rebbe replied, “Talu b’Hergesh,” it depends on your feeling. Chabad Chasidim didn’t decide things based on their feelings. The Rebbe’s advice here is not suggesting “relying” on your feelings rather telling you, as a Jew, chasid and Lubavitcher, you should have feelings for these types of things! Then you’ll know whether or not to say Tachnun.