DPP4 and COVID-19: Neurovascular disorders may play a role in driving the progression of post-COVID-19 fatigue, with SARS-CoV-2 infection and the role of DPPIV as a co-receptor potentially causing tissue and cellular damage, as well as exacerbating inflammatory or autoimmune responses due to disruptions in the proteolytic enzyme activities, catalysis, and molecular signaling pathways.