Thanks for the query to H.C.M. Forum.
In my opinion such type of weakness within two days of fever
is not possible .
As you mentioned that there is excruciating pain , unable to walk.
In my opinion get in blood for Dengue
fever , Chikungunia fever .
Also get in blood for C B C and hemoglobin
Consult a physician and get his opinion for complete check up. Good luck. Dr. HET