Weight loss in a dream commonly reflects a sense of release -- shedding a burden, a habit, or an old self-image you no longer need to carry with you. It often surfaces after letting go of something significant, marking a lightness you're just beginning to feel in your waking life.
When Mars, lord of the ascendant, shall be posited in the tenth, it confers on the native dignity and power; which will be accompanied with injury and cruelty; and may therefore be said, a misfortune, rather than happiness. - William Lilly (1602.-1681.)