Only the pilot knows he is in cloud, the aeroplane does not so the same rules apply; pwr + att continues to equal performance. If the aircraft is well trimmed and in balance the performance will remain constant. If the performance is constant the power and attitude are correct.
Gertrude the Wombat introduces an important human factors issue. Even in VMC we use our senses in a ratio of approximately 60% sight to 40% of other senses. So when we lose sight or, in this case, the sight information received by the brain is unusual, we become hyper sensitive to the other senses and so can soon become disorientated. The senses within the inner ear and "feelings" can become so strong that belief in the attitude instruments may be lost. The sensors in the inner ear become our primary source but erratic and continuous movements of the head will aggravate. Reliance therefore must be on the aircraft performance; speed, altitude and heading. If they are all good then leave the aeroplane alone. Any corrections if necessary must be small and never rushed.