and a terrible pain in diana's shoulder is taking its toll. >> it feels like it's going to come out of the socket. >> but still she pushes through, driving her body forward. it's not easy. simply keeping her body fueled is a delicate balancing act. even getting her something to drink can be a challenge. >> a special mix. we're looking for 20 ounces and she's been doing about 24, which is really good. >> he rigs a line to drop the pouch of fluid into the water. >> i'll blow the whistle. she'll see is trailing by the strip there and she'll pick it up and drink out of it. >> now rehydrated, diana takes just five more strokes and then crisis. >> bonnie, bonnie. >> you see, diana is getting enough fluids. but now she's not getting enough oxygen. so team nyad snaps into action.