I think QCQ and Kamil have given you the answer's that you need to fix your problem. Hunting from an elevated treestand take's lot's of practice ,it become's very easy to drop your bowarm when shooting at your target .Being elevated make's you not want to bend at the waist thinking you may fall . I've had this problem it's happened to me .
Bend at the waste and keep your bowarm straight . That's the trick to making an accurate shot
One other thing is when your aiming at your deer or what ever you may be hunting you have to visualize where you want your arrow to exit ,this meaning you want to aim a little lower on your target . you want to aim where you want your arrow to exit .I hope you aren't confused by this and it sound's weird ,but it is the way you can assure success next time .

nubo