Yes, he was sick. Why do you think he was coughing up blood? Tsukiyomi's side effects aren't coughing up blood. Plus Madara even told sasuke, he was sick, and was prelonging his life with medications, so that he'll be alive when Sasuke gets stronger so he could die fighting Sasuke, knowing that sasuke got strong. He only wanted the best for his brother, thats why he told Sasuke to kill his closest freind (Naruto) So that he can get MAnekyou Sharingan. Itachi wanted sasuke to become STRONG, so he could be safe.