Do the herbs which promote relaxation in certain herb teas have more efficiency when theyre warm/hot as opposed to cool/cold?
We're hard-wired to relax with warm drinks, right from our very first hours with mom, so of course, warm beverages tend to be more relaxing than cold ones.

Now for the physics of it all: Heat is an indication of the energy in any given substance. The energy determines how active (and reactive) it is. That is why sugar dissolves more quickly and completely into a hot liquid than into a cold one. When we smell any odor, it is actually molecules of the substance escaping into the air, coming into contact with our nasal sensory apparatus, and being translated by our brains. The hotter the beverage, the more molecules escape into the surrounding air. The more molecules escape the beverage and make contact with our sensory cells, the stronger the smell will be. The more aromatic the tea and the more reactive it is, the greater effect it will have.