The epinephrine can cause all sorts of reactions like shaking, racing heart, faster breathing etc... My mom went through a biopsy for breast cancer. They took a biopsy from the breast and one from the axillary lymph nodes. When she put her arm down she felt some tingling and then the nurse told her she could get up and get dressed. As soon as she stood up she began shaking all over and fell over. The nurse actually scolded her for overreacting. The tingling apparently just came from holding her arm up. Later when we all went in for the meeting with the oncologist, I sat reading the report. I could not help myself and started to laugh. Not at my mom, but the plain ignorance or stupidity of the medical team who had come up with one excuse after another. They inserted a double dose of epinephrine into my 100 lbs mom, one in her left breast and the other under her arm, both obviously right by her heart. No wonder her heart was racing and she was shaking. At least we resolved the mystery and my mom decided to go get treatment somewhere else where the medical team would respect her enough.
Shaking can also be a sign of anxiety. If I am nervous, anxious, or scared I will immediately start shaking.
According to Peter Levine's book "Waking the Tiger" shaking can also occur as a part of healing. It's basically the body's own way of getting rid of the adrenaline that we PTSDers have way too much of floating around in our systems. The body runs through different stages during trauma. Shaking or tremors complete the full cycle, explaining why people who were not able to react through flight or flight and instead froze or were kept immobile are more likely to develop PTSD whereas people who can react physically are significantly less likely to develop PTSD. The final step of the circle is shaking to get get the adrenaline out. After that happens the animal who was threatened in the first place is usually fine and gets up and finishes whatever it was doing prior to the attack. I thought that was an interesting visual and as I have learned in therapy basic defenses years after the trauma (e.g. kicking or punching) can still help complete the cycle and free me of the stuck PTSD symptoms. After the kicking or punching I usually go through some shaking.
At the moment it still feels like I have to go through each individual trauma separately and with my CPTSD this will take quite a while, but according to my therapist at some point the learning will begin to affect different traumas at once...