Already nauseated, it didn't take much. The normal disorientation of changing location had Itachi gagging. He staggered away from Shisui, managing to drop to his knees before he vomited again, this time more dry heaves than actual vomit as he gagged and gripped the cold toilet seat to keep from tipping in.
Itachi leaned forward, gagging on nothing and shaking.
Then he realized he was crying. Half the gags had probably been attempted sobs. He was dirty. Shisui had pulled his hair. Shisui was going crazy. His scalp still ached, because Shisui had pulled hard.
And Itachi was just scared. Scared with no real reason behind it. Just scared.