A person should place his head on his left arm (unless his arm has tefillin on it – then he should use his right arm) to say Tachanun. This is done if he is in a room with a Sefer Torah. If he is in a place without a Sefer Torah, he should still recite Tachanun, but should do it without putting his head on his arm.
4. Be kind to yourself. Speaking badly even about yourself is unethical.
הלכות שמירת הלשון 