赶紧 in a hurry
“赶紧” is an adverb that means “doing something against time or in a hurry”, usually put before a verb.
I noticed that “福” was put upside-down, so I said hastily, “福 is reversed!”
“一下子”, adverb, means “in a very short time”and is usually put before a predicate adjective or verb.
At this moment, I suddenly realized why Dad had put the character upside down.