The fact that there is a very specific time frame when you have this issue, between 4-7, would make it seem likely to me that there is probably some underlying reason other than a general anxiety or panic disorder. It may not be totally obvious, but if there is a time frame, it would be worth keeping a diary of your daily activity so that it can be analyzed. It may be something environmental or something you consume hours earlier contributes. Perhaps you have been in a standing position for a long time and then go to a sitting position or vice versa and you have some sort of circulatory system/cardiovascular change going on. Perhaps your blood sugar has dropped and you need to eat. As Christina said, perhaps that's when a medication is wearing off. Perhaps a million different things... It would be very hard to sit here and guess. The answer may not be totally obvious even to you.

Now that is not to say that one cannot have bipolar and anxiety/panic attacks. I have Bipolar, PTSD, OCD traits, and Panic Attacks without agoraphobia. Some people have complicated histories and have multiple things going on. I'm not saying it is impossible to have both. If you feel like you are experience anxiety attacks, go talk to your doctor. They have a set of questions they can give you to help decide if it is a situation that they can diagnose you with and treat.

But because you seem to have such a narrow time frame or repetitive time frame where you are experience these symptoms, do consider keeping a diary to help you and your doctor see if you can figure out a cause. The good news with that is that if you can determine a cause, you can usually just make an adjustment and things will improve. At the end of the day that's what you want- to figure out whatever it's going to take to make you feel better. <3