One saying that is often used in medicine is that "common things are common." In your specific situation, this means that there is probably a very simple explanation for the increased stiffness that you have been feeling. Perhaps you changed your bed, your pillow, or your chair at work? Perhaps you started a new work out routine? Perhaps a new medication that you started is having side effects? Or, perhaps you are just experiencing normal aging. The key to all of these is that there are some rare reasons that can be causing common problems. For that reason, seeking the advice of a physician if your problem persists is important. A physical examination by a licensed physician will give you the peace of mind that you are well, or uncover further issues that may need to be examined. Stiffness can sometimes be a sign of rheumatologic disorders, muscle disorders, or just about anything else. It is a very vague symptom, that usually is only of value if there are other symptoms such as focal pain or swelling, fevers, weight loss
, or fatigue that are also present. Regardless, please see your doctor
as a starting point. Good luck.