It has been simplified.
1.traditional characters.:擔心
There is no “sunrise” at all. :D
擔:carry sth by shoulders ,心:heart
so, 擔心 literally: carry one's heart by shoulders
If you carry your heart by your shoulders, not put it inside your body, you must be worried. 放心(not worried ),literally : put heart down
擔= 手+詹
擔=to carry sth. by shoulders
手=hand,詹=to talk too much ;foot
I don't know how could it mean "to carry".It looks confusing.
2.simplified characters 担心
As Edward said, 旦 contributes to its sound. 擔 in 擔心 sounds like dan1(pinyin) and 旦 sounds like dan4. Thus the authority simplified 擔 into 担. It's easier to write but not quite different. (the left parts are the same)