In LoZ, your sword only shoots lasers when you're at full health, which gets pretty annoying after you get lots of health containers (more health to fill up just to use this attack). You most likely weren't at full health when you fought Aquamentus, and when you die and respond, you only get 3 hearts no matter how many you have, meaning you have to keep filling up your heart containers to full every time you die.
Also, this thread belongs in the Zelda Game Help section.