Hypovolemia and orthostatic hypertension
The pathophysiology of orthostatic hypertension has not been elucidated. It is believed it involves activation of the sympathetic nervous system [1], vascular adrenergic hypersensitivity and diabetic neuropathy [2]. High levels of plasma atrial natriuretic peptide and antidiuretic hormone were observed in children [3].

Hypovolemia causes:


baroreflex-mediated increase in muscle sympathetic nerve activity [4]
release of epinephrine and norepinephrine [5]
activation of renin-angiotensin axis [5], thus increasing ADH levels


All these reactions result in vasoconstriction and blood pressure raising. But not up to absolute hypertension.


  Orthostatic hypertension is diagnosed by a rise in systolic blood pressure of 20 mmHg or more when standing [6].


This is possible. A raise of 20 mmHg from hypotension could result due to vasoconstriction.



References:


Fessel J, Robertson D. Orthostatic hypertension: when pressor reflexes overcompensate. Nat Clin Pract Nephrol. 2006 Aug;2(8):424-31. doi: 10.1038/ncpneph0228. PubMed PMID: 16932477.
Chhabra L, Spodick DH. Orthostatic hypertension: recognizing an underappreciated clinical condition. Indian Heart J. 2013 Jul 5;65(4):454-6. doi: 10.1016/j.ihj.2013.06.023. PubMed PMID: 23993009. 
Zhao J, Yang J, Du S, Tang C, Du J, Jin H. Changes of atrial natriuretic peptide and antidiuretic hormone in children with postural tachycardia syndrome and orthostatic hypertension: a case control study. Chin. Med. J. 2014 May;127(10):1853-7. PubMed PMID: 24824244. 
Ryan KL, Rickards CA, Hinojosa-Laborde C, Cooke WH, Convertino VA. Sympathetic responses to central hypovolemia: new insights from microneurographic recordings. Front Physiol. 2012 Apr 26;3:110. doi: 10.3389/fphys.2012.00110. PubMed PMID: 22557974. 
Wikipedia contributors, "Shock (circulatory)," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Shock_(circulatory)&amp;oldid=612494727 (accessed June 26, 2014).
Wikipedia contributors, "Orthostatic hypertension," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Orthostatic_hypertension&amp;oldid=603984647 (accessed June 26, 2014).