I'm currently running a campaign and I have two casters that can cast healing word. And whenever I had a big melee enemy reduce them to zero HP by pounding them into the ground, they bounce back up straight away with this spell. It feels like the spell is making it too easy for them to win battles with monsters that are of the melee type, and it makes the fights less exciting.
My issue is that the mechanics of health and combat in D&D 5th edition, allow for the Healing Word spell to be exploited in this way. This way, there are no negative side effects for being reduced to zero HP this way. No loss of actions for the healer or player that was reduced to zero hp.
A very good explanation about this exploit is given in the taking 20 channel.
So my question is:
since the combat and health mechanics are somewhat responsible for this exploit, how could these be changed to counter it?
I want having your character be reduced to zero HP to have an impact again. At least more than that can be countered by a first level bonus action spell. I'm not looking for changes in the spell (as is suggested in the taking 20 channel)
EDIT: Thanks for all the responses, But i would like to add that I'm not really discussing the spell, but rather the health and combat mechanics, and what kind of changes that could be done that could make encounters like these more challenging.
To clarify my issue with the healing word spell, I'll try to explain it with an example:
When I have a 50 hp fighter at 1 HP, and he gets hit by a enemy for 20 something damage, he is reduced to 0 HP. The giant effectively deals 1 damage. Next the healer casts as a bonus action the healing word, giving the fighter 1d4 hp. The healer only needs to be in 60' and be able to see the fighter to heal him. After the healing word, the healer still has his action and move available. He can cast a cantrip and move away. Then it's the fighter's turn. He gets up without any problem and attacks the enemy. This can repeat so long the healer has level 1 spell slots available. Effectively the enemy has downed a player, with his action, while the party loses no actions because healing word is a bonus action.
This would be less of a problem if there is only one healer with the healing word spell. The enemy could walk to the healer and start attacking him, if he manages to close the distance. But in my case the second healer can heal the first healer in a similar fashion, and I have two fighters in the group so the enemy needs to finish them both off before he goes after the healers. But they never go down for good, as they can always get up the next round. In effect the party can fight any single melee enemy this way with relative ease, with the use of just one first level spell. The link I provided gives a good explanation of how this work, and why it is can be problem.