Claimant seeks review of an order of the Workers’ Compensation Board affirming the referee’s determination that her knee injury is not compensable. The evidence is undisputed that claimant fainted and fell at work while checking groceries. The Board found that claimant had failed to meet her burden of showing that the fall was work-related and was not caused solely by a condition personal to claimant. We reverse and remand.
Claimant testified that she had stayed home from work for two days because she had the flu.1 On the day of the injury, she requested permission to take another day off to recover, but her supervisor said that he would “really appreciate it if [she] could make it in,” because the store was short on employees. She testified that she went to work in a weakened state because of the flu and that her condition intensified as the day went on. She also stated that the work was hectic and stressful and that she was working two cash registers at the same time. She described how she became nauseated and light-headed and called her supervisor, asking to be relieved.2 The supervisor arrived and helped the customer at claimant’s second register. Claimant then collapsed to the floor on her knees. The supervisor testified that he continued to help the customer at claimant’s register and, when he saw that claimant was too dizzy to get up by herself, he called another employee to help her to the employees’ room. After that day, claimant’s right knee continued to hurt, and it eventually required surgery.
A compensable injury is “an accidental injury * * * arising out of and in the course of employment.” ORS 656.005(7)(a). A work-related injury is compensable, even if it *483is otherwise unexplained. See Phil A. Livesley Co. v. Russ, 296 Or 25, 30, 672 P2d 337 (1983). However, the fact that an employee is injured on the premises during working hours does not by itself establish a compensable injury. A claimant must show a causal link between the injury and the employment. 296 Or at 29.
Both the Board and the dissent contend that claimant did not establish that her injury was work-related, because the fall was unexplained. Nothing is unexplained. Claimant, who had asked to take the day off because of illness, was summoned to work by her employer, who knew that she was ill. She went to work in a weakened physical condition and was required to perform stressful work activities. The fact that she fell at work was not merely fortuitous. There is no evidence to support the Board’s finding that claimant’s work did not contribute to her injury.
Reversed and remanded for reconsideration.
In oral argument, counsel for employer conceded that claimant’s ailment was not a complex medical condition that required expert testimony to establish it in the record. Therefore, claimant was competent to testify at the hearing about how her condition impaired her ability to perform her job. See Uris v. Compensation Department, 247 Or 420, 427, 427 P2d 753 (1967).
Specifically, claimant testified:
“It was really, really busy that day. I — like I said, I ran two checkstands, and with the — we had them lining up, and I was going as fast as I could go, and I started feeling a little nauseated, kind of lightheaded, and so I called * * * my boss at the time, on the intercom, and I said, I’m feel [sic] kind of nauseated, a little dizzy; can you please come get me out of the checkstand?”