That is called a startle reaction. It is not a phobia. Severe startle reactions are often related to childhood trauma.
It is quite like Lygophobia, which is something coming to get you in darkness- I have this!
This is not a named phobia. The fear of surprises is Kainolophobia.
acrophobia
Demophobia or Agoraphobia
The irrational fear is called a phobia; the experience or object that triggers a phobia could be called a phobic experience or object.
There are two different words for someone who does not feel fear. People who are fearless are called non- fear phobia and non- exit- phobia.
An irrational fear of gravity is called barophobia. Someone who has this phobia usually fear that they might be crushed by gravity, gravity might cease to exist or that gravity will cause them to fall.
The fear of someone watching you is called Anatidaephobia.
Althaiophobia is fear of marshmallow'sAlthaiophobia~fear of marshmellow's
Phobias are an anxiety disorder in which someone's fear of something is extreme and irrational. The phobia of cockroaches is called katsaridaphobia.
I'm not sure if there is such a phobia but the phobia of people is Anthropophobia.
Mud Phobia is the phobia (fear) of mud. Its called mysophobia, myso meaning mud and phobia meaning fear.
There is no medical term or phobia name for the fear of immigrants.However a similar phobia called Xenophobia is the fear of foreigners.
If failing is your fear the name for the failing phobia (phobia mean fear) is atychiphobia.