I fully understand what you mean. I am the same way. Usually, for the most part, I handle my anxiety fairly well during the day. But it seems like after around 5 pm I get soo much more jittery, anxious, panicky. I think the reason for that is, as others have mentioned, it is dark outside. I truely believe that weather, and light and darkness, can affect the way you feel. For me it is usually after my kids go to bed that I feel most scared. They usually go around 9-10pm, and then the house is sooo quite and it just seems like an invitation for your mind to run wild.
I usually TRY to use this time for prayer, and Bible reading. Although somtimes it is hard for me to calm down enough to concentrate on what I am reading. I just ask God to help me...grant me some peace so I can get a good nights rest. I try to remind myself as well..I was pretty much ok during the day, so I just KNOW how I am feeling now is nerves...nothing is going to happen to me, and I can rest knowing God is watching over me. It does eventually work because I do get to bed and sleep usually an average of 6 hours or so. Like it says in the Bible..the battle we wage is one of the MIND. I think it is amazing how our minds have so much to do with how we feel. Sometimes at night..I try not to FIGHT the panic soo much..as to just let it run its course..knowing that it is not something that is going to kill me..but it will work its way out of my system eventually.
Just the other night I started feeling as if my heart was going to beat out of my chest. I started getting all worked up and scared of having a heart attack. So I started to pray...telling God I know He is with me..etc. and I told myself...I KNOW I have had this symptom before, and I am still living..so it is most likely not anything serious. I just kept repeating that to myself over and over and then it just started to slow down( my heart) and before I knew it..the whole 'spell' was over. The more you let the symtoms get the upper hand..the longer it will last and take control.