Venom (the symbiote) is literally driving Eddie (the host) crazy by compulsively hunting all night, so that Brock can’t ever sleep.
Over the course of issue #1, we see Venom becoming increasingly savage. Brock tries to soothe him with a twinkie.
Yeah, that doesn’t work.
During earlier minis, Venom has been talking about eating brains. In issue #1 he finally really does it. Brock is horrified by what they’ve done, and resists turning into Venom again–so the Symbiote leaves him.
The story reveals that the symbiote has an alien hormone structure, and drains its host of a particular biochemical. Once that chemical is depleted, it must eat brains.
Brock goes nuts, escapes from an asylum, dons military gear, and goes Venom hunting.
Brock has identified a synthetic source of the hormone, which enables him to reunite with the symbiote–now that they both need each other to be whole, they can’t be separated again without going nuts.
I don’t know if this was intended to be an allegory for addiction, but it works well when you read it that way.
It’s also nice to have a Venom series that’s just him–no other symbiotes. Much more of a character-based interlude before they all come back, along with Wolverine, in the next mini.