Some negotiations can be very emotional. Rights allocation, estate allocation, and family law topics are good examples. Taking a break in these circumstances is perfectly reasonable. Sometimes this tactic is used on purpose to be unsettling, such as if someone infers that they need a break before they become too angry to reel back.
Someone may say, “You are getting emotional. Let’s take a break.” This may be a fully reasonable response or it may be manipulation; the difference is tone. If accusatory, it is a tactic. If empathetic, it may be genuine.
If you need a break to compose yourself, say so. As hard as it may be, you must wipe away the impact of the tactic. Acknowledge it, map the next steps, and send a signal you are still in the game. “Yes, I am emotional, and we may need a break, but you need to address how what you are requesting is unfair.”