It is plausible. Dick was known to consume large amounts of amphetamines, and amphetamine use significantly increases the risk of stroke.

"He clearly descended into abuse after his fourth wife left him in the early 1970s. Afterward, according to Kyle Arnold’s biography, he was taking speed by the handful. “He stuffed his refrigerator with thousand-pill jars of amphetamines” and “told his mother he consumed a thousand-pill jar per week.”" https://www.thefix.com/philip-k-dick-s-high-life

"Conclusion Increases in stimulant drug abuse may increase the rate of hospital admissions for strokes and stroke-related mortality." https://jamanetwork.com/journals/jamapsychiatry/fullarticle/...