Because when brian had woken up and was thirsty it reminded him of a time him and terry we're lost in the woods which brought up the thought of a nostalgia memory
Realised needs to be changed from the past tense to the present tense so that it is realise. In this case, the verb is part of a prepositional phrase and is being used to talk about moment within a story set in the past.
Have forgotten needs to be changed to had forgotten since it is a past action that happened before another action in the past.
Bought and got need to be changed to buy and get so that the sentence is parallel. These words are part of a series of actions that starts with the wake.
