Hello Eva,
There can be various causes for the numbness in your forearm like a cervical disc lesion which may cause numbness togetger with pain in the neck or shoulder radiating down the arm and forearm, local nerve causes like median nerve entrapment and ulnar nerve injury which causes numbness also in the hand, or atherosclerosis (clogging of the arteries) which may cause similar symptoms, or diabetic neuropathy along with deficiency of vitamin B. Sice you also have dizziness, a cervical disc lesion is still likely for which you can do a Ct scan or an MRI of the cervical spine.
You can also consult a neurologist to discuss the symptoms and may go for blood tests for diabetes or do muscle conductivity and nerve velocity tests.
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