Go to the next page. First symptom is a drooping eyelid (6)

'drooping eyelid' is the definition.
(I know that drooping eyelid can be written as ptosis)

'go to the next page first symptom is' is the wordplay.
'go' indicates an anagram (I've seen 'went' mean this ('go' can mean move)).
'the next' is a charade indicator (letters next to each other) (I've seen this in other clues).
'page' becomes 'p'.
'first symptom' becomes 's' (1st letter of 'symptom').
'to'+'p'='top'
'top' is an anagram of 'pto'.
'pto'+'s'+'is'='PTOSIS'

'a' is the link.
I am not very happy about this link. It may be part of another bit of the clue.

Can you help me to learn more?