Woe is me - what does it mean?

Solution 1:

Woe is me!

Lack-a-day.

Misery me,

These are all morose phrases, They can be strung together, or prefaced by Ah, or Alas, but apart from that whatever the grammar, they are unalterable. Don't try Woe is he! or Lack-a-year.

The tone is archaic, often self-deprecating, and mock-heroic.

Solution 2:

woe is a noun/interjection meaning misery, sorrow, misfortune, etc. (Note that this is different from the homophone whoa which is a command to, eg, a horse, to stop.)

"Woe is me" is an idiom likely borrowed from hundreds of years ago (hence the odd syntax) which could be read as "Woe has befallen me". In other words, I am suffering (or about to suffer) some intense misery or misfortune.

Whether the syntax is broken or not depends on how you look at it. One can argue that saying "Woe is me" is saying that I have (metaphorically) become woe (ie, misery) or vice-versa, which is legitimate, both in syntax and semantics. But it's not the sort of syntax one would use in a business letter.