Single Judge Application; flare-up; this Court’s caselaw and VA guidelines requiring VA medical examiners, in situations when direct observation is not possible, to opine on and quantify the effect of pain on functioning based on other evidence. See, e.g., Sharp v. Shulkin, 29 Vet.App. 26, 35 (2017) (instructing VA examiners, when conducting examinations that do not take place during a flare-up, to “offer flare opinions based on estimates derived from information procured from relevant sources, including the lay statements of veterans”);