Don t panick. I did that already... You need to disconnect the cable and take out the battery. Then you press on the 3 buttons for a while (to empty the note completely) and put the battery back in. When you press the 3 buttons again it should be in download mode again.
To me it happened i think due to the fact i didn't tick update boot loader in odin 1.85. After ticking it and flashing no problem any more. Good luck