They only knew that sentinels could enter their manic state once there were too many pollutants in their mental sea and if the pollutants in their mental sea were extremely agitated, the sentinels couldn't suppress it at all.
In the battlefield where the sentinels were always exposed to the pollutants, it's not surprising to have sentinels being on the verge of their mania one after another.
Those on the verge of mania could certainly feel it; that's why they would immediately drink stabilizers so that they wouldn't enter their manic state.
That's also why they were all rotating to rest so that they could properly manage their condition.
If they weren't in a very desperate situation, those soldiers wouldn't let their conditions escalate to their manic state.
If they're in a desperate situation, those that were nearing their manic state might form a death squad to deal great damage to their enemies; however, the battle situation was good.