I've suffered from grief before. To me it's a medical condition, which someone can suffer from after something terribly bad happens or is witnessed by someone, where the brain needs time to put strong feelings in order, to organise the painful feelings, allowing someone to move forward. It can cause 'shock', shaking, dissyness, nightmares, headaches, tears, depressed feelings, lack of energy, lack of clarity, lack of sleep. If the symptoms persist in the months after the incident it's important to seek medical advice, as if you consider to suffer without medical help it can lead to ongoing depression. The way it felt for me was like temporary mental disfunction.