(My answers are intended as information and opinion only. I am not a Dr. or a licensed psychologist and can not offer counseling or medical advice.)
I'm sorry to hear you are suffering and I hope we can find a way to help alleviate the sadness you are experiencing. If I understand correctly, you have not heard anything at all from him for the past four days. A day before that (which would be five days ago), you sent him a text that he replied to. I want to make sure I am clear on this and that you haven't received a single text from him in that past four full days. Is that correct?
When we last left off, you told me he had requested a week or two to "clear his head" or however he phrased it and then he said you guys would talk again. The plan was for you to give him that space he requested, and not contact him for a week. I'm thinking you weren't able to do this? Please don't misunderstand my question. I am not judging you or implying you have failed in any way. I know how hard it is to not make any contact with someone you love and are thinking of literally 24/7. I totally get it. I'm just asking the question to try to understand what his experience has been like this past week. There is a reason that is important.
It's important because if he doesn't have that space and time away from you like he requested, then he won't truly experience what it is like to not have you in his life. Every day you make contact, you provide him with a level of contact that allows him to feel as if you are still there and puts all the power in his lap since he now gets the choice of whether to reply or not. That whole process fills the void that would exist otherwise if you were making no contact at all. So ironically, by continuing to contact him to try to get him back, you are robbing yourself of the opportunity to let him realize that he misses you.
Your question asked above related to how to deal with the feelings you are having due to his lack of contact. I'm going to be very honest with you and not sugar coat things. These type situations are definitely stressful and you are undoubtedly going to be sad and anxious while it plays out. That is ok. It's normal. I think the key is to give yourself permission to be sad, or anxious, or angry or lonely, or whatever emotion arises. Don't be emotional about your emotions. In other words, don't get down on yourself because you are sad. Don't be angry at yourself for being lonely. Let yourself feel whatever it is you feel, and know that although it doesn't seem so right now, these feelings of sadness and anxiety will eventually pass.
Do your best to stay active, engage with friends and family, do things like go to the movies, exercise, write poetry, go shopping, read a good book, get your nails done, get a massage, take a hike in a pleasant outdoor area, etc. These are just examples and you can decide to do whatever it is you like doing. It may be some of these things, or none of these things. My point is to just keep engaged with life and don't let the sadness you will feel overwhelm you or cause you to just curl up on the sofa and be paralyzed. Like I said, in the end, however this works out, you are going to be OK. Believe that, and it will give you strength to endure what may be a difficult time should he decide he truly wants to end the relationship. I'm not saying I think he wants to end it, but I am saying it is of course a possibility. Only time is going to tell.
My advice would be to give him a solid week of absolutely no contact from you at all. To give yourself peace of mind and to make sure you feel that he knows what you are feeling, first send him a final text. Tell him that you miss him, you love him and you wish he was back in your life. Then say that you know he needs time to think, so you aren't going to reach out to him any longer so he can have the time and space he has requested. End it with saying you hope to hear from him soon and that you'll be waiting. Send that and then end all contact. Not a single text, no emails, no phone calls, no talking to anyone he knows to get a message to him. Remove yourself from his life for just one week. Let him really feel what life is like without you. If he truly loves you, he will miss you and he will eventually call you. He knows how you feel and your final text as referenced above leaves little doubt or room for interpretation.
If a week goes by and he has not made any contact, then you have a serious question to ask yourself. That is, "Do I really want to chase a man who doesn't want to be with me?" I know this is a very hard question to answer, since logic will tell you that you of course do not want to pursue him, and your heart will tell you to pick up the phone and call him no matter what. I can't make the choice for you, but I will say that as hard as it may be, no man (or woman) is worth chasing to the point that they are refusing all contact and you are out there daily trying to reach them. For me, it really boils down to that old and corny mantra that goes something like, "If you love something, set it free. If it comes back to you, it is yours. If it doesn't, then it never was." Like I said, it's kind of corny, but there is a definite message to be learned from it. You deserve to be in a relationship where you are pursued by your lover equally. You deserve a man who wants to fight to be with you, not one who wants to purposely avoid you. You deserve a man who will dialog with you and inform you honestly of why he feels the way he does, not a man that leaves you high and dry with little to no explanation. It's going to take courage and strength for you to resist desperately chasing him, but if a week goes by and you receive no contact, I would recommend trying to hold out for one more week. If he fails to contact you ever after two weeks, then my feeling is you have received all the answer you need. Yes, you will be sad during this process and you will be sad if the result is that he doesn't make contact. However, I feel that being sad for the short term while your heart heals is better than being in a relationship for the long term with someone who is simply not worthy of the time and love you are investing.
I really hope this helps and feel free to contact me again if you need to chat.