He notes that the economic recovery was fast when a shock was caused by external factors but took time when it was by internal ones. For details, see Krugman, P., "The Audacity of Slope: How Fast a Recovery?" webinar held by the Princeton Bendheim Center for Finance, May 15, 2020, 1:14:19, https://www.youtube.com/watch?v=h1ZiTIou0_8. 6  aggregate demand or aggregate supply.
That said, making such distinctions is not that simple because aggregate demand and supply are related to each other.