"Ridha" is derived from radhiya yardha meaning accept something sincerely without feeling frustrated or depressed. Related to Iman, ridha is devided into two kinds, Ridha of Allah to His servants, and ridha of His servant to Him. As Allah hinted in His firman " .... Allah being pleased (ridha) with them and they with Him ..." (Qur'an 98:8)
However, ridha doesn't means accept anything without motivation to change the fate or get something better. Someone who ridha with what Allah has given to him still must have motivation to get something better.
Ridha is being pleased with taqdeer that Allah has written to us, but not being pleased with naseeb that happen to us. If we get sick we should not ask 'O, Allah, why you give me an illness?", but also we should not being pleased with the illness and thinking "I ridha with this illness and I will not cure myself".
By the way, there is a story related to ridha. One day Umar bin Khattab was walking when suddenly the rain fell. Umar immediately ran for shelter. Someone saw it and asked him "O, Umar, why do you run away from Allah destiny?". Umar replied "I run away from one Allah destiny to the another His destiny". (Source : https://www.islamicboard.com/ )
Its not easy sometimes, but with The Almighty by our side, nothing seems impossible. He will indeed heal me, heal you and heal us. No matter what we are facing, i wish that all those pain akan Tuhan angkat slowly. insya Allah amin.