Did you just spend time creating one thing (like working on a complex aec item) to realise you deleted something else a little ways back accidently. Here's a trick I remembered whilst fiddling with the roof object.
I had just created a new shape and had spent some time editing and experimenting (fiddling). Now I had what I wanted. But I had damaged another roof and I didn't know what I did. So I Cntrl-C'd the new object and then Cntrl-Z (undo) back to restore my original object. Then I just pasted back in the new object! That was easy! Probably only works on a dumb object like a roof or acad objects though. A more complex object like a curtain wall assembly would assume the paramaters of the style set in the drawing. To use this trick for a styled object like a curtainwall object you would need to change the style name slightly before pasting it back in, thereby preserving your latest adjustments.
Mike Williams has just reminded me about the 'OOPS' command, which will restore the last deleted object which may help you in a different situation.
All tricks & tools for your enjoyment!