redundancy. Doesn't your language have words that mean the same? It's called synonym. And, as we see, most of them just mean the same in a particular context, but have different nuances. It gives you an option to express yourself deeper. And, since words like "to do" or "to go" can be used as synonyms for about 50% of the words of the English language, how would that look if all your sentences were "I do this, then do that etc."?
The name شادي is actually masculine. Thus, نَعْسان was used.
And by the way, the whole sentence here is not good Arabic. It sounds like Syrian/Lebanese dialect of Arabic. In standard Arabic, we don't combine the possessive suffix ـك (or others) with question articles like كيف (how) or أين (where) ...etc. Combining these is done in dialects not in good standard Arabic.