I have been having difficulty with memory. some days i feel like i have brain fog. almost like my head is numb. i will mess up sentences and have a hard time comprehending. is this something to be concerned about?

It is not feasible to provide an opinion without additional history, physical examination may be some tests. It would be prudent to see your doctor to see if you may be depressed. Depression is treatable. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated. Drink more water. Wish you good health!

Multiple causes of "brain fog", including medication side effects, use of recreational drugs, sleep deficiency, thyroid issues, vitamin deficiency, Celiac disease, depression, etc. Since this prompts concern on your part, would likely benefit you to sort this out and have your doctor evaluate you.