he felt ill,so he went to the hospital是并列句还是复合句?

1.he felt ill, so he went to the hospital
因为有连词so的存在,因此为并列句且前后为因果关系.
2.he went to the hospital because（as) he felt ill.
是复合句.因为句中的because引导时间状语从句,实际上是一个句子.