You would think that a rather banal series that has a fantastic premise and was subject to a Gag Dub would be bereft of Nightmare Fuel. Unfortunately, Sealab 2020 takes a realistic look at how dangerous an underwater laboratory would be.
- Time and again, characters take the bends very seriously, insisting on use of compression chambers. One student in the first episode outright explains what the bends are, even saying that the bends can kill you. He says this while smiling .
- In "Deep Threat", several tanks of radioactive waste were leaking into the ocean. Worse, Bobby and Sally try to investigate by themselves, eventually getting lost. Bobby also comes very close to running out of oxygen.
- "Lost" involves a red tide, which depletes the ocean of oxygen. Meanwhile, Gail befriends a dolphin, but that dolphin eventually goes head-to-head with not only the red tide but also a shark.
- "Green Fever" involves the lab getting a crack that is leaking water into the underwater lab. Meanwhile, one of the workers undergoes Sanity Slippage by being underwater so long, and eventually starts damaging electrical equipment and tries to "free" someone recovering from surgery.
- "Where Dangers are Many" involves a mining machine that is not only destroying the underwater environment but also disturbing the wildlife.
- "Backfire" continues the above trend with underwater oil drilling instead. Worse, the drillers have official permission to drill, while a lot of damage is being done with the Sealab crew arguing with the drillers.
- "The Deepest Dive" has some of the crew dive into deep depths with a newly-made underwater vehicle. Unfortunately, a giant cephalopod wraps its tentacles around the vehicle, which is losing oxygen and electricity. Any attempts at freeing itself from the cephalopod only damaged the vehicle.
- "The Challenge" has Alex explore a sunken ship because he wants to find treasure. Unfortunately, instead of following proper protocol, he rushes into the ship by himself. Eventually, the ship starts collapsing with him being trapped under fallen lumber. Even after a member of the Sealab crew manages to free Alex, the two still need to be properly rescued out of the ship.
- "Collision of the Aquarius" involves a submarine crashing into a rock wall, damaging its nuclear reactor. On top of a threat of a nuclear meltdown, Captain Murphy keeps fighting with the commander, who wants to go to the reactor directly, risking death.
- "The Capture" has Bobby and Sally try to free some animals from cages. Unfortunately, they got trapped in a dolphin trap, which drags them near a cliff and far away from contact with Sealab.
- "The Artic Story" is about a couple of researchers trapped in a research facility blocked by an iceberg. Then the temperature of the facility starts dropping... Appropriately, one of the researchers actually gets a nightmare over their possible deaths.
