Conversation so far:
When did Chrisye get sick?
In July 2005 Chrisye was admitted to Pondok Indah Hospital.
What was Chrisye's ailments?
Chrisye was admitted to Pondok Indah Hospital, complaining of breathing difficulties.
What else was wrong with Chrisye besides breathing difficulties?
After 13 days of treatment he was moved to the Mount Elizabeth Hospital in Singapore, where he was diagnosed with lung cancer.
Was Chrisye's lung cancer treatable?
Chrisye underwent the first of six rounds of chemotherapy on 2 August 2005.
Where did Chrisye undergo the first of six rounds of chemotherapy?
Chrisye was moved to the Mount Elizabeth Hospital in Singapore.
Did Chrisye stop after the first round of chemotherapy?
Chrisye underwent the first of six rounds of chemotherapy.
What happened after Chrisye's first round of chemotherapy?
Chrisye underwent the first of six rounds of chemotherapy.
Did Chrisye get sick again after chemotherapy in 2005?
By February 2007, Chrisye's health was again in decline.

Question: When did that start?
Self-contained rewrite: When did Chrisye's health decline start again?