To understand this, one should first understand the function of cytochrome c oxidase. It is the last enzyme in the mitochondrial electron transfer chain whose function is to transfer the electrons from cytochrome c to oxygen molecule converting oxygen to water molecules. Now, there are 3 componenets required for this reaction: cytochrome c having extra electrons, a functional cytochrome c oxidase and oxygen molecule. Decrease in concentration of any of these components would result in similar symptoms. At high altitude, the level of oxygen is low. Due to this less oxygen is transported to cells resulting in less oxygen molecules available for transfer of electrons. This results in slowing down of electron transfer resulting in above symptoms. Cyanide on the other hand, binds with cytochrome c oxidase and renders it non functional. The enzyme is no longer able to transfer electrons to oxygen again resulting in slowing down of electron transport chain and similar initial symptoms. Remember, electron transport chain is like a line of men transferring load from one place to another. Unless the man gives his load to next person, it can not take more load from previous man resulting in slowing down of transfer. Therefore, cyanide poisoning starts with same symptoms as altitude sickness.