Also, I have had an immense amount of pressure in my head sometimes so it causes a headache.
Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
You have a constellation of symptoms that are difficult to localize to one neurological cause/syndrome; thus, there is a broad differential as you mention in your title.
In the majority of cases muscle twitches are benign meaning that they are of no consequence and are not resulting from a serious cause. In such cases, the twitches may be related to anxiety/stress, caffeine, and often occur after recent strenuous activity or muscle over-use. It is important in such cases to reduce stress/anxiety levels and to reduce caffeine intake. Tremors of the hands can be physiological that is exacerbated by stress/anxiety and caffeine.
Anxiety is a psychological and physiological condition that can present with a multitude of symptoms. They include heart palpitations, muscle tension/twitching, fatigue, nausea, chest pain, shortness of breath, headaches, and GI symptoms such as diarrhea to name a few. Anxiety can also be accompanied with panic attacks such as a feeling of impending doom or death. If diagnosed, it usually takes time for you and your physician to find the optimal pharmaologic agent to help with your symptoms.
Another condition called benign fasciculation syndrome (BFS) is a condition in which there are involuntary twitches of various muscle groups, most commonly the legs but also the face, arms, eyes, and tongue. If the diagnosis is confirmed and other causes are excluded, it can be safely said that the likelihood of progression or occurrence of a serious neurologic condition is low. When BFS is present but not particularly bothersome or disabling, treatment is not necessary. If severe and it requires treatment, there are a few medication options though this condition is not very common, and the research that has been done on its treatment is limited. Minimizing caffeine and stress, and treating anxiety if it is present, will improve your symptoms.
Other causes of twitching have more serious consequences, but they are usually in association with other neurological findings such as progressive weakness. An example of this category is ALS.
Since you have a history of prior head trauma, I would encourage you to discuss your symptoms with your physician. You would likely benefit from a complete neurological evaluation (from a neurologist). He/she may order an EEG and perhaps an MRI of the brain based on what is found during the assessment.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.