Marek Grzezulkowski, aged 42, was driving a Mercedes Sprinter box van when he hit the woman on Fishmore Road, Ludlow on New Year's Eve, 2021.
Telford Magistrates Court heard how the woman had travelled on the train with her bike from Leominster to Ludlow, before taking to the road.
Grzezulkowski's dashcam footage showed that he nodded off to sleep before waking up as he crashed into the woman.
She suffered an injury to her forehead the size of a £2 coin which required 15-20 stitches and plastic surgery to close up. She was given a full body scan, which found she had a "cracked" kidney. She is waiting to see if any further treatment will be required.
The victim also had severe grazing to her toe and knee, heavy bruising to her inner thighs and "severe pain" in many areas of her body. She also described having mood swings during the month after the crash happened, although no brain injuries were discovered.
When police officers searched Grzezulkowski's van, they found 14 joints of cannabis. He was arrested and interviewed twice by police. He accepted he did not see the bike and that he had taken cannabis. A test found he had 4.2 microgrammes of Delta 9 THC, the main psychoactive component of cannabis, in his system - more than twice the legal limit of 2mcg.
Grzezulkowski, of Canterbury Leys in Tewkesbury, Gloucestershire, pleaded guilty to causing serious injury by dangerous driving and possession of cannabis. His lawyer accepted the circumstances were too serious to be sentenced at magistrates court.
Grzezulkowski will be sentenced at crown court at a date to be decided. Magistrates made him subject of an interim driving ban and granted him bail ahead of his sentencing.