RERA (respiratory effort related arousal)
Breathing becomes harder without stopping completely, and the brain notices and wakes up for a moment. It is not remembered the next morning, but sleep has been broken up.
A little more detail
A respiratory event lasting at least 10 seconds, with increasing respiratory effort or flattening of the nasal pressure curve and ending in an arousal, that does not meet the criteria for an apnea or hypopnea. The AHI plus RERAs gives the respiratory disturbance index (RDI).
Source: Berry RB, Budhiraja R, Gottlieb DJ et al. Rules for scoring respiratory events in sleep: update of the 2007 AASM Manual for the Scoring of Sleep and Associated Events. J Clin Sleep Med. 2012;8(5):597-619. doi:10.5664/jcsm.2172