ANSWER - There are a couple of different ways to answer this question. Firstly there is the question of your own sub conscious mind. It is possible that in the relaxed and magical head space generated by spell work, you imagined the knocks. It is also possible that you made the link between knocks caused by an innocuous external source (neighbour using a hammer for example, that sort of thing) and believed it to be the result of your workings. If this was the case in the second incident where you heard a single knock, you may have panicked as the link had established itself in your mind and you believed you had made a contact with a spirit.
But the second explanation is just as likely and this is that your workings were genuinely overlooked by a spirit. In the first case you felt the spirit was benign and safe to be around and in the second instance you were warier and did not feel a positive connection with the spirit. This would explain why you felt such fear the second time but no fear on the first occasion. Now the important thing about this explanation is that it is crucial that you understand you have not summoned a spirit or invited it into your home. The spirit is not a permanent entity and presents no threat to you. It was likely just a passing entity, attracted to the energies of your magical workings.
I see no significance in the number of knocks, often a spirit will respond to a question as instructed - you may say knock once for yes or twice for no but as you were not intentionally making contact I do not think you can attach much significance to the number of knocks. If I am right and your workings were observed by two separate entities then it is not surprising that they both have different ways of making themselves known to you.
So in answer to your question, was it acknowledgement, very possibly it was. You could have been getting a little encouragement or a thumbs up from your spirit friend. If you had any uncertainty about what you were reversing, it could have been a little nudge by a passing spirit to say you were doing the right thing.
It is never right or wrong to feel fear and I would never presume to tell another person how to feel. I do however strongly suggest that you consider the fear you felt and think about ways to minimise it in future. Are you casting your spells in a protective circle? Are you ensuring your own energies are grounded first? Are you aware of how to protect yourself from malign spirits? If you have doubts about what you are doing, these doubts make it easy for your fears to be played upon. When conducting magic, be confident in what you are doing and in what you are hoping to achieve and if you are uncertain, don't do the spell until you are certain.
I actually think you dealt properly with the circumstances on both occasions. You did the right thing to remove yourself from the situation when you felt uncomfortable, it enabled you to gather your strength, see the situation in perspective and go back to conclude your work properly. This is always the best thing to do if you make contact with anything you don't have a good feeling about. Be polite, be decisive and walk away.
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