Heedless Resurrection

Q: Can I sacrifice Ledros to play Watcher from the discard pile?

Yes.

Q. You have a Bewitching Spirit at a battlefield. You play Heedless Resurrection, killing the Bewitching Spirit as part of the additional cost to play the spell. Can you play the same unit from the trash that you just killed?

No.

355. Playing a Card

1. Remove the card from the zone you are playing it from and put it onto the Chain.
2. Make relevant choices
3. Determine Total Cost.
4. Pay the card's costs.
5. Check legality
6. Finish finalizing this card and proceed with the card's category of Play.

Also, you can play the unit to the battlefield, even if Bewitching Spirit was the only you had there, as the game is in a Closed State thanks to Heedless Resurrection being on the Chain.

187.4 If a player has no Units at a Battlefield and the turn is in an Open state, they loose Control of that Battlefield in the following cleanup, unless there is a Combat or Showdown ongoing there.