welcome to healthcare magic forum, in these cases mosltly it is synovitis
it is accompanied arthritis
,it dissappears because the synovial fluid
acumulated in synovial
pouch which is located between the joint and has a pouch which does absorb the fluid which is generated but this execcive generation of fluid is due to erosion or pressure in the joints but exrecise also promotes fast absorption of the fluid generated
so you do not feel it but actually you are having erosion of joints,please sleep keeping
your levs elevated and consult with an orthopaedician for follow ups.