Un espasmos de mi brazo derecho

Mi brazo derecho tiene espasmos recientemente.  

Recientemente/Últimamente tengo/he tenido espasmos en mi brazo derecho.

No sé por qué.

Me pregunto por qué.

¿Qué habré hecho?

Jugué "Punch out." Es un juego de Wii.

Quizá sea por eso.

¡Pero el juego es muy divertido!

English translation.

Title : Spasms in my right arm

My right arm have spasms recently.

Recently/Lately,  I have/ I have had spasms in my right arm.

I don't know why.

I wonder why.

What have I done?

I played "Punch Out." It's a Wii game.

Maybe, that's why.

But the game is very fun!

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1)
I was confused with this sentence : 

¿Qué habré hecho? = What have I done?

Qué = What
habré = have
hecho = done, fact

"Habré" indicates "Future" so it literally means "What will I have done" in English. 

However, it seems like "One of the uses of the future tense in Spanish is to show conjecture(臆測、推測)."

http://www.spanishdict.com/answers/109282/future-tense-to-show-conjecture-qu-habr-hecho-con-las-llaves

2)

Quizá sea por eso.　=　Maybe, that's why.

Quizá = Maybe
sea = ?
por = for (prep.)
eso = that (pron.)

What is this "sea"?

It's "ser" in Spanish = "to be" in Englsih

      Subjuntivo (Subjunctive 仮定法)

• Yo 　　　　　　       sea
• Tú 　　　　　　       seas
• Ella/Él/Usted      sea
• Nosotros 　　     seamos
• Vosotros 　　　   seáis
• Ellos/Ustedes 　sean

In this sentence, I am talking about "maybe" so that is probably why I need to use "sea"(Subjunctive).

http://www.studyspanish.com/lessons/subj1.htm