How do I tell them I'm just tired? or can I call it burn out?
Why not tell them the truth? Explaining to them just how you did here with us in your post.
Seems to me that "I feel tired" may indeed not be the best excuse to call in sick for work... however, the fact that your motorcycle is broken and needs fixing is a valid excuse for being late or not being able to go to work one day. So, I suggest you go with that (or, if this is in retrospective, that was what you should have done).
An honest, yet valid and effective message to send could be (or could have been):
Hello [HR or person you are writing to].
Sorry for writing at this late hours, but after leaving work today my motorcycle broke half way on my way home. After several hours I managed to get home, but I need to take my bike to the mechanic to give it a proper fix.
Thus, I won't be able to arrive at work, but I will surely be able to be there tomorrow after it's fixed.
Thanks, threeFatCat
Edit:
So, after a bit of clarification seems that your situation is the following:
First, you wrote HR last night telling them that you "were not feeling well", and that you won't be able to go to work today.
The truth was that you were actually tired, because of your motorcycle breaking down in the middle of the night, and you having to fix it, and you having to go to the mechanic today.
Now, you want (why?) to write a follow-up message to HR stating that you will be arriving to work tomorrow.
Unless you are bound to write that follow-up message, I suggest you actually don't write it, and just be there at work tomorrow. TheThen, if/when they ask you details on what happened you can tell them the whole story, and that you "weren't feeling well" because of everything that the bike incident represented.
...now... if you actually wrote "I am feeling sick" then I fear you are now trapped in the endless loop that lying involves... try not to do that in the future.