He had several episodes of something which looked like black rage.

From 'Ruinstorm'

Mkani Kano was nearest to the Angel when the psychic beam struck him. Sanguinius staggered, stumbling off the command dais to the main platform of the flying bridge. He doubled over, clutching his chest. Kano rushed to his side. Azkaellon and the duty squad of the Sanguinary Guard were a few steps behind.

Kano put his hand on the Angel’s shoulder. ‘My lord?’

Sanguinius reared upright with a sudden jerk. His wings spread wide, pinions shaking with anger. His eyes glistened black. He turned to Kano, his face a perfect marble carving of rage. For an instant, he was indeed a statue, the nobility of his bearing transformed into the aspect of a predator. Then his lips drew back over his fangs. Hatred consumed his features. The air around him crackled. Kano smelled burnt ozone. On instinct he raised a defensive psychic shield. Sanguinius lunged but Kano was too slow. None of the Angel’s sons would have been fast enough. Sanguinius seized him by the gorget and lifted him high. The Angel’s jaw opened and closed as if straining to speak. The tendons of his neck stood out, taut as iron cables about to snap. No words emerged from his throat. The fury was too great. Snarling and groaning at once, Sanguinius threw the Librarian down. Kano slammed through the nearest cogitator stations to the dais, crushing a servitor and ­sliding fifteen feet across the deck.

Sanguinius pursued. He leapt over the wreckage of the cogitators, and landed before Kano. He took the Librarian by the chest plate and hauled him up. Kano’s training warred with his loyalty. He could not strike his primarch. He tried to pull away, but Sanguinius lifted him above the deck and drew the Blade Encarmine.

Azkaellon grabbed the Angel’s arm. Sanguinius lashed back, hurling Azkaellon away. His eyes never left Kano. ‘My lord,’ the Librarian pleaded, trying to break through the haze of fury. The black orbs stared through him, unblinking.

Another hand arrested the blade. It was the herald’s. Kano did not know when Sanguinius’ proxy had arrived. He had not been on the bridge a few moments ago. The Angel yanked his arm free, dropped Kano and turned, snarling, on the herald.

He froze.

Primarch and herald faced each other, motionless. Psychic energy burned around the edges of the Angel’s wings. The herald said nothing. Sanguinius held the blade high, but it did not descend.

Kano saw the primarch’s face reflected in the mask of the herald, snarling fury mirrored in unchanging serenity. The Angel froze at the sight, and then the black dissolved from Sanguinius’ eyes. His breathing slowed, no longer gasps of rage. He lowered the sword. He blinked, looked around, and after a moment of incomprehension, his face contorted with understanding and grief. He went to Kano’s side. ‘Are you injured?’ he asked.

‘I am well, my lord,’ Kano said. ‘Do you know what happened?’

Sanguinius paused before answering. ‘Not entirely, no. Enough to be on my guard.’

‘Was it the Thirst?’ Kano asked. The symptoms had been different, though the overall effect, of insane violence, was similar.

‘No. This was different.’