Of course it can exist in a physical form, something that prevents you from actually writing, perhaps caused by a repetitive strain injury or broken fingers. The term is commonly used to express a feeling of panic or anxiety when you sit at your keyboard or with a pen in your hand, and don't have a clue what to write. A bit like an actor on stage forgetting his lines. It's a mental thing. But hey, you CAN still write.
Your Writer's Block is caused by idea that today you have to write a chapter of your novel, or a verse of your poem, or the conclusion of your short story, or something completely new and meaningful. You've made an appointment with yourself and have fixed your mind on completing this task. But the fact is, the creative mind can't be tied down to these time constraints. It's true that you should write something every day, but it doesn't have to be the thing that you had scheduled at the end of your writing day yesterday. Learn to be more flexible.
So you don't have broken bones, or RSI, you've been for your run, or a cycle, or done some yoga, or had a sleep, and you're sitting back at your desk. Panicking.
Instead, try writing random words. Things that pop into your mind. Still can't get that self-imposed deadline out of your head? Then write down things you see around you in the room or out of the window. A string of nouns with no relation to each other apart from the fact they are part of your environment. Take those words you just typed on the screen or wrote on your pad: 'Desk', 'Mug', 'Pen', 'Hobnobs', 'Tree', 'Lawn', 'Dog poo', and write a sentence or two about them. Totally random sentences. Add sensations - sounds, smells, feelings. See? You CAN write!
You won't have what you think is Writer's Block every day, so this exercise may not be repeated for many weeks, by which time the Hobnobs will have been eaten and replaced by a plate of fresh fruit, and the dog poo will have been cleaned from your lawn to be replaced by a carpet of autumn leaves. Next time you think you have Writer's Block, simply write words. Remember, five-a-day is better than none, but I'm sure you'll find you can manage at least a hundred.