I have a buddy who did the same thing.
He came to work the next day and said he thought he tore something, and then asked me what I thought as the flopped his foot around. He said that he had worse pain from a sprain, and the biggest problem he had was his foot flopping around as he walked. I told him I would think he would be in excruciating pain if it were torn, so it probably was not, as he just had a dull ache, but go see a doctor if he was concerned enough to ask me about it, as engineers don't give out the best medical advice.
He went to see the doctor and sure enough his achillies was completely torn and he had to have the tendon reattached, go through the cast, therapy, etc.
I still amazed he did not feel much pain.
