The West Yorkshire-born star, 35, posted a video on Twitter telling fans that he became ill as a result of food poisoning, combined with his Crohn's disease, and that he ended up in hospital.
He said the side effects include "a bad type of arthritis that's affected all the joints in my body".
The star, from Bradford, posted the video, explaining "what's been going on in my life over the past eight months," hours after sharing a picture which showed a shocking change in his appearance.
"I've been keeping a bit more of a low profile as I got really sick and ended up in hospital last summer due to a really bad type of food poisoning, which having Crohn's disease ... is a very bad combination," he said.
"Thankfully the NHS worked amazing well to get me out of hospital and back on my feet."
He said he was still dealing with some of the side effects.
"The main one is a bad type of arthritis which has affected all the joints in my body, my toes, my knees, my neck, ankles, my hands, which really sucks as a magician when you can't shuffle a pack of cards cos your hands are in so much pain, which has happened on the odd occasion."
He said he was working with doctors and physio, and "doing everything in my power to get myself to 100%".
"As you can see, my appearance has changed quite a bit due to all the medication I'm on ... I'm on quite a lot of tablets," he added.
As well as the extra weight, he said the medication had left him with a rash "all over my head ... all over my body".
Dynamo added: "I'm doing everything in my power to get myself better. I wanted to let you guys know what was going on from me personally.
"I'm staying positive, I'm working on new magic, I've got great people looking after me and I know you guys who have supported me from day one will have my back."