sumiran literally means "to remember", but has a special meaning in Indian spiritual traditions. Duhkha/Sukha are two sides of the same coin, or dualities. Man tries to grasp the "positive" side of the duality while trying to escape the "negative" side, leading to suffering.

Kabir Saheb exhorts us to remember this very fact when we're happy, and not get carried away thinking that it will last forever. This remembrance is sumiran of the Truth. The one who does this will not suffer.