The 37-year-old star recently finished up the Progress tour with the band and said he was feeling the strain as they approached their last show.
He wrote on his blog: 'Since Denmark there has been nothing in my tank. I couldn't feel my legs. No power. No strength. No real energy. To be the flailing banshee that I wanted to be. Just vapours.
'Did I panic? No. I relied on the energy of the audience. The energy of the five boys in unison. Did my body write a few cheques it couldn't cash? Yep. Will it take me a few weeks to feel normal? Yep. Do I care? Nope.'