The campaigning mum-of-two who is in the US where she is taking part in a clinical trial of a new drug has been experiencing debilitating side effects in recent weeks.
Vicky is hoping that the trial involving the drug M7824 which is being directed by the National Institutes of Health in Maryland will prolong her life.
However, she confirmed in a video message on Thursday that she had spent three nights in hospital receiving treatment after falling ill last week.
She wrote: "It has been over a week since I last posted an update. There's a very good reason for the delay. I have been very, very sick. I became very ill, very suddenly on Saturday evening and it escalated very quickly into being unable to bring down a raging temperature.
"I spent three nights in hospital until they figured out what infection was causing the spiking temperatures which kept coming. Once again, it is a side effect of the main drug that caused me to be so ill.
"The drug, M7824, can cause inflammation in any part of the body. I developed Bell's Palsy (inflammation of the facial nerves) last week and then this week, the inflammation went to my sinuses which were all extensively inflamed and which led to me getting so sick on Saturday.
She continued: "I am home now recovering and on an antibiotic to treat the sinus infection which is slowly improving. I still have to go back in to hospital tomorrow for my treatment because I was too sick on Tuesday to have it.”
In a new update she said this was “the reality of taking part in a clinical trial”.
“It has been a very, very low week for me and has made me think long and hard about whether I will continue on this in the long run. I need to start seeing better results soon in order to make all of this hardship worth it,” she admitted.
However, with her focus on returning home in July and seeing her family and friends, Phelan says that her visit is giving her cause for optimism.
"While I dread the thought of having treatment tomorrow, the ONLY thing keeping me going is the knowledge that this is my LAST dose of treatment before I go home next month."
She added that she will not make any further decisions, as she focuses on spending time with her family and friends.
"I am looking forward to a break from it all for a month and to spending time with my kids and my family and friends,” she added. “Big decisions can wait until I come back.”