word problem - Guess the object - What Am I Riddle (Part 3)

I'm lying down, with a dah-ditty-dah, in the middle of the end,
I'd hang upside-down similarly with my friend,
Were I to flip over, with a dah-ditty-dah, it'd be the middle of the day,
Right way up I cannot plainly say,
Here's the key, let's end the fun,
I'll tell you a secret, I hide behind one

What am I?

Part 1
Part 2

Answer

Answer:

! (exclamation mark)

Explanation:

Lying down in the "middle of the end" (n = -· in morse code)

Upside-down in friend
Flipped over in the "middle of the day" (a = ·- in morse code)
Right way up I cannot plainly say (one does not speak "plainly" when using '!')
Here's the key... Hide behind one - (think "keyboard")