You can differentiate between your thoughts and a spirit's telepathic messages to you because a spirit's message is going to be random and seemingly pops into your mind. Even if the messages come through in your own voice, it can be a message or thought from a spirit companion or guide. There are times when you will have thoughts or messages from a spirit, and it will be in their own voice, but it will not always be that way. You can always ask a spirit companion for confirmation that they are communicating with you if you don't feel comfortable enough to judge if a spirit is communicating messages.