A popular YouTube science content creator, who once celebrated receiving a Covid-19 jab despite it causing her severe arm pain, is now in the throes of a devastating debilitating illness.

"Physics Girl" Dianna Cowern, who has over 2.6 million subscribers on youtube, issued a shocking Twitter update Monday informing followers she's suffering from severe MECFS, or chronic fatigue syndrome (Myalgic Encephalomyelitis).

"My condition has declined fast. It's clear I have severe #MECFS," Cowern tweeted.

"I can't eat solid foods, or feed myself. I have moderate pain almost 24/7. I have trouble breathing and lose my ability to stay fully conscious when my symptoms intensify. I cannot leave the bed."

"I am scared," she admitted.

Previous Twitter updates show Cowern's health has been on the decline, with a post last month revealing she was unable to shower standing up.