I get comms as dps when I throw in a joke or two, say hi, really anything to break the monotony of low level leveling roul dungeon.
Sometimes I also get one because I just happen to be the second to last guy to exit and the last guy threw it to me (probably)
To all the healers that I should have commended:
When things go smoothly, I get to see more clearly who is pulling their weight and commend accordingly.
When things go nuts and the healers really pulling their weight, I become too focused on keeping myself alive and doing damage. I do not know how much great healing you are doing because I am in tunnel vision mode. Then I just threw the commendations to one of two healers...