Sources said 29-year-old Pistorius was stricken with remorse for shooting Reeva three years ago.
One said: “Somehow it unleashed even more pain and emotion in him. Oscar was hysterical.
“Reeva would have been 33 and it triggered all the images, memories and horrific moments when he shot her.
“I believe he asked to have candles to light for her birthday but of course he was refused.
“He has refused food and is refusing to do anything.”
Pistorius was later seen by a counsellor and medics.
He is serving a six-year sentence for murder but this Friday prosecutors will argue at a court in Pretoria, South Africa, that he should be jailed for longer.