Sounds like a generic term meaning 'we don't know'
This is from the OED
b. Hence congestion of an organ: an abnormal accumulation of blood in its vessels, by which its functions are disordered.
1803 Med. Jrnl. IX. 325 The second or local Sthenic Congestion is_one of the most frequent causes of Apoplexy.
1845 G. E. Day tr. Simon's Anim. Chem. I. 265 Blood was again taken, in consequence of further symptoms of congestion.
1875 B. Richardson Dis. Mod. Life 65 The diseases included under the names of catarrh, bronchitis, congestive bronchitis, congestion of the lungs, pneumonia.



