“Fallen” is episode one of season seven of Stargate SG-1.
In the season six finale, “Full Circle”, Daniel tried confronting Anubis – who was revealed to be a partially Ascended Goa’uld (or maybe that should be a partially un-Ascended Goa’uld?) – and stopping him from attacking Abydos. He failed, as the other Ancients stopped him. Now, he’s re-appeared as a normal human on another planet, albeit as a human who doesn’t know who he is.
Jonas has figured out the translation relating to the Lost City of the Ancients – and he thinks he knows how to find the gate address. SG-1 go through to the planet he thinks was it – the same planet where Daniel has just appeared. Perhaps not a coincidence.
Daniel, despite having lost his memory, also says that Jonas’ translation was wrong. SGC needs to find this lost city, and its stuff, as quickly as possible, before Anubis comes knocking. They come up with a risky plan to take a single starfighter, fly through the enemy starfighters, and then destroy a ventilation shaft on the Death Sta… er, Anubis’ mothership. Yes, there are similarities, and yes, they do seem deliberate.
Daniel’s Ascension, and un-Ascension, didn’t make a lot of sense really from an internal point of view, but it was governed by real-world factors, not in-universe ones.