[He does pull back a little, taking a breath, trying to push back the anger and fear, because shouting at her isn't going to change what happened. He knows that. He's just. Incredibly upset.]

According to Spock, initiating a mind meld when you don't know what you're doing can cause a neural disease called Pa'nar Syndrome. The synaptic pathways start to degrade, and the endocrine and immune systems are also compromised. It's a very serious condition if left untreated, but fortunately- [Considering there had been no guarantee they'd ever see Spock again when he vanished, and he didn't want to think about what would have happened if he didn't.] Spock was able to cure him before it progressed too far.