Detained Nasser Zefzafi was attending a hearing at a court of appeal on Tuesday morning with 53 co-defendants when he said he "felt faint", Abdessadek El Bouchtaoui told AFP. The judge halted the hearing.
An unemployed 39-year-old, Zefzafi became a leading figure in Al-Hirak al-Shaabi, or the "Popular Movement" that broke out in late 2016, calling for jobs, unemployment and an end to graft in Morocco's neglected northern Rif region.
Zefzafi - who was arrested in May after allegedly interrupting a preacher at a mosque to call for further protests - launched a hunger strike last Wednesday along with some 30 other detainees.
It was Zefzafi's first such strike since his detention.
Other jailed Hirak activists earlier held a month-long hunger strike which they suspended in October.
They face trial on various charges including "undermining the internal security of the state".
Rights group Amnesty International says authorities have arrested "hundreds" of Hirak demonstrators, including minors, and that over 400 remain in custody.
A Moroccan court last week sentenced El Mortada Iamrachen, a member of the movement, to five years in jail for "defending terrorism" and incitement over comments on Facebook, Moroccan media reported.
Originally sparked by the death of a fishmonger crushed in a rubbish truck as he tried to salvage a confiscated fish, the Hirak demonstrations snowballed into a major challenge to the authorities.
In response, security forces launched a crackdown, slinging the alleged leaders of the mainly young protesters in jail in May and June.
The Rif has long had a tense relationship with the central authorities in Rabat, and was at the heart of Arab Spring-inspired protests in Morocco in February 2011.
King Mohamed VI relinquished some of his near-absolute control through constitutional reforms following those protests.