How can I get curl to resume download after waking from sleep mode?
You could try using wget -c:

-c
--continue
    Continue getting a partially-downloaded file.  This is useful when you
    want to finish up a download started by a previous instance of Wget, or
    by another program.  For instance:

            wget -c ftp://sunsite.doc.ic.ac.uk/ls-lR.Z

    If there is a file named ls-lR.Z in the current directory, Wget will
    assume that it is the first portion of the remote file, and will ask the
    server to continue the retrieval from an offset equal to the length of
    the local file.