Thank you for your query.
If two pregnancy tests are negative, chances are very very less that you are pregnant.
Confirmatory would be a blood B HCG test or an ultrasound.
Please go for one of these to allay your anxiety.
Also, the symptoms you describe sound like a syncopal attack.
Reasons could be hypoglycemia
, sudden hypertension
, heat stroke, sudden vasovagal shock
Please go for a complete examination and blood work.
ALso, rarely, an ectopic pregnancy could present in this way.