Curing A Case Of Laziness (怠け病をなおすでござるの巻) is episode 15 of the 1981 Ninja Hattori-kun anime.
In the middle of the night, Kenichi is having nightmares about Kemumaki. We then get to look into his mind and at his dreams. His first dream shows Kenichi being forced to massage Kemumaki's shoulders; when Mr Koike passes by, Kemumaki switches places with Kenichi, and Mr Koike has a go at Kenichi for taking advantage of Kemumaki. His next dream shows Kemumaki nicking Kenichi's test papers and threatening to show them to Mrs Mitsuba. He then lies to Mr Koike that Kenichi was beating him up. Kenichi desperately tries to convince Mr Koike that he's innocent, but suddenly he wakes up. He is relieved that it was all a dream, but he can't face the prospect of going to school, so he fakes sick. Mrs Mitsuba and Hattori try to get him out of bed, but he pretends to have a stomach ache as well as a headache.
Meanwhile at school, Mr Koike is marking the register and draws light to the fact that Kenichi is absent. Yumeko assumes that he is unwell, but Kemumaki is disbelieving and, as an ulterior motive, decides to nip over to Kenichi's to discover the truth. Back at home, Hattori confiscates Kenichi's comic book. When he hears that Kemumaki has arrived to check on him, he pretends to have a panic attack, so Mrs Mitsuba sends Kemumaki away. Having left the house, cheeky Kemumaki rings for an ambulance, leading it to Kenichi's house. Kenichi is relieved that he's being left alone at last, but then he sees the ambulance and is knocked for six. The paramedics examine Kenichi, who says he's fine after exercising. As they leave, Hattori reveals the truth to Mrs Mitsuba - Kenichi is faking his illness. As comeuppance, Mrs Mitsuba has Hattori disguise himself as a doctor, and Hattori tries to vaccinate Kenichi. Alarmed, he runs off, causing a wild goose chase that also sees Kemumaki being roped in to help Mrs Mitsuba and Hattori catch Kenichi. When Kenichi finds Kemumaki in the park, Kenichi tearfully forgives Kemumaki and the story ends.