Final answer:
The protocol for losing sight of a dive buddy includes searching briefly at depth and then ascending to the surface to reunite while ensuring gradual and safe ascent to avoid decompression sickness.
Step-by-step explanation:
In a night diving situation like the one described, the primary concern should always be safety. According to standard scuba diving procedures, if you lose sight of your diving buddy, you should search for a minute or so while safely at the same depth. If you cannot find them, the next step is to perform a safe ascent to the surface where you should attempt to reunite. It is critical that divers always surface slowly and safely to avoid decompression sickness, keeping an eye out for their buddy as they ascend. Ascending immediately after only 5 minutes may be a bit quicker than recommended, unless other circumstances call for it. It is also important for divers to have pre-dive communication concerning such situations and to consider carrying equipment such as surface marker buoys (SMBs) for visibility on the surface, as well as practicing buoyancy control and being aware of the dive environment.