Sorry to hear, but we've all had similar experiences. Here is a checklist:

1. Are you hunting with the same apparrel that you practice with? This one got me after 20 years of bowhunting this year on a miss I had. I had on a pull over hood, that changed my anchor point at full draw, I missed (glad I did w/o wounding) low and left. Even gloves, or bulky clothing can change things ALOT.

2. If you are 12 ft or over, its very important to bend at the waist when shooting at a deer. If not 6-8" high is not uncommon. Its hard to know if you even did in the excitement, its something that needs to be practiced. Sometimes, brush, or tree limbs can cause you to distort your form significantly, effecting arrow placement.

3. Was your arrow nocked where it should be? If the arrow slips on the string in your excitement, a high or low shot will result.

4. Did you hold at full draw a long time? Sometimes, "forward creep" will occur if you did. Its Important that just prior to release - you pull back all the way again, and settle at your normal realease point. If the arrow is released forward of your normal anchor point, a high shot can result.

5. Someone already mentioned it - maybe the deer was closer than you realized.

6. If you are hunting extra high, or on a downhill slope, gravity tends to work with the arrow speed, meaning that you might have to use your 10 yd pin, at 20 yds to compensate. A pendulum sight, or again, practice from high up will help.

Regardless of whether any of these things are the result or not, its important for you to fing out the cause. Shoot a few practice shots from the same stand, see if you hit where you want to.

Good luck