Four short lines carry a surprisingly big reaction. The speaker has received a single text message from someone, and it has stirred up an enormous tangle of feeling: ten thousand emotions, as they put it. The number is obviously an exaggeration, but that's the point. It captures how one tiny message can set off excitement, worry, longing, and confusion all at once.
The last line, "I hope you're happy," is where the tone gets interesting. It could be read as teasing, a half-joking "look what you've done to me." It could also be a little bitter, as if the speaker is annoyed at being thrown off balance. The poem doesn't tell us which, and that ambiguity is what makes it work. The mood is wry, vulnerable, and a bit overwhelmed. The speaker clearly cares about this person, and the plain, casual wording makes the feeling seem honest rather than dressed up.