There is a problem I encountered recently. My DM rolls initiative for groups of monsters together. We are at level 4, so Sleep should be a decent battlefield control.
However, we have been encountering too many enemies recently. Due to the action economy, a dozen goblins is really hard to survive, and the DM thinks we can manage because my bard can put almost all of them to sleep. And I can, but the key point is that almost all of them is not all of them.
Last time I put to sleep 5 out of 6 enemies. On their next turn, the one that remained awake, woke up his colleague. And then the freshly woken up guy woke up the next. And so on, until all were awake and standing. My teammates were tied in other corners of the room and couldn't help, so for me nothing changed; in that round I did nothing to the enemies, they did nothing to me, and I was down a spell slot. It was a disappointing outcome.
Is there a way to prevent this, and make Sleep an effective spell again?